Die Design Fundamentals by Paquin

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DIE DESIGN FUNDAMENTALS

DIE DESIGN FUNDAMENTALS A step- by- step introduction to the design of stamping dies including material, plJnches, die sets, stops, strippers, gages, pilots and presses

J. R. PAQUIN · Regi stered Professional Engineer Supervisor, Tool Engineering Department Cleveland Engineering Institute Senior Member, ASTME

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643~ INDUSTRIAL PRESS INC . , NEW YORK, N. Y. MACHINERY PUBL I SHI NG CO., LTD ., BRIGHTO N I , ENG LAND

FIRST EDITION -

FOURTH PRINTING

Cop righ © 1962 by The Ind ustr ial Press, New York 13. Pr inted in the United Sate s of America. All right s reserved. This book, or parts thereof, may not be repro ce in any form without permission of the publi shers. Library of Congress Cmalog Card Number: 62- 19251

Preface This book is a more comprehensive compilation of the information contained in a series of articles that appeared in American Machinist/ Metalworking Manufacturing under the title , "Fourteen Steps to Design a Die". The number of illustrations and the length of the text have been almost doubled. The series was well-received. A large number of requests for additional copies of the magazine installments showed that a definite need exists for a book of this type . Inquiries came from students; from draftsmen, tool designers, die designers, toolmakers and diemakers. They came from virtually every state and from a number of European countries. Some arrived from India and Japan. Many requests for additional copies came from instructors in technical schools who found the material helpful in their classes. This book was written by a member of the tool engineering profession whose practical experience has spanned more than twenty years. He was formerly Tool and Die Designer for such companies as Republic Aircraft Corp., Frigidaire Division of General Motors Corp., Underwood Corp., Torrington Manufacturing Co., and Associated Engineers. He was formerly Chief Engineer of Worcester Automatic Machine Company. The terms of the book are those that die men are familiar with and understand. In addition, over eight years of teaching prospective tool and die designers have provided insight into the special requirements of students. The plan of the book is unique. After the introductory material, the design of a representative die is separated into fourteen distinct steps . Each division or step is illustrated in two ways; 1. As a portion of an engineering drawing. That is, as the component is actually drawn on the die drawing. 2. Pictorially, to improve the student's visualization. In succeeding sections of the book , each step in expanded and explained in detail as it is applied in the design of various types of dies. The final section shows the twenty types of dies in use in industry . Line drawings are given both a pictorial view and a conventional two-view or three-view engineering drawing. Thus, the student sees, three dimensionally, just how the component appears and how it must be visualized in designing. At the same time he learns exactly how it should be drawn on a die drawing. Thus students are exposed to accurate and proportioned data and this becomes their experience.

v

It has been the author's intention to present th e information about fundamentals of die design in the form of underlying principles. After an analysis has been conducted to identify the principles involved, each is clearl y explained with appropriate illustrations and text as a complete unit of informat ion presented -in the modem picture-story form. The engineering princi ples then stand out clearly for adaptation to an unlimited variety of die designs. Num bered s ide headings are used to provide a quick and easy reference fro m text to illu s tration an d vice versa. Mathematics is an indispensable ally of any ty pe of mechanical desi gn. It is the cement that fixes the relationship between all the parts of any mechanical assembly and it determines the shape, size, and strength of each of the components, as well as the clearances between the m. The elements of mathematics required for the desi gn of die components have been introduced throughout the book where required for solution of specific pr obl ems instead of being grouped together in a final section that would be too often overlooked or neglected. The author is pleased to acknowledge the valuable contributions made by many friends and associates in the preparation of this book. First among them is Rupert Le Grand, Senior Associate Editor of Am erican Machinist/ Metalworkin g Manufacturing, who provided encouragement in developing the articles in th e series. Mr. Le Grand's perceptive suggestions and able editing of serial installments helped materiall y to establish direction . Special credit is due to Isaac Hart and Charles Zelenko, Directors of Cleveland En gineering Institute for their encouragement. Robert Leuthner, Registrar, and V.J . Costanzo, Instructor extended many courtesies . E.E. Kalman made finished drawings for a number of the illustrations and for the problem book. Messrs . Robert Moyer, Charles Einsiedler , and Lester Horne of Standard Die Set Co., Providence, R.I. provided assistance in development of Sections 13 and 14. Considerable material was originated as a resu lt of questions posed by the author's former students in the tool and die design classes of Porter School of Tool Design, Hartford, Conn., Worcester Junior College , Worcester, Mass., and Cleveland Engineering Institute, Cleveland, Ohio. Credit is also due to Professor Casimir Rakowski , Department of Mechanical Technology, State University Agricultural and Technical Institute, Farmingdale , N.Y., who conducted a penetrating review of the book in manuscript form. Many press and equipment manufacturers contribut ed photographic illustrations. Each is acknowledged where the illustration ap pears in the book. Special credit is due to Robert Rhodes of Federal Press Co., Elkhart, Ind ., and to E.C. Monell of F.J . Littell Machine Co., Chicago, Ill. , who contributed outstanding line drawings of press and equipment construction for Section 2. J .R. Paquin Cleve lan d, Ohio july, 1962

vi

Contents Section

Page

1 - Introduction to Die Design . . . . . . . . . . . . . . . . . . . . . 2 -

1

Presses and Press Accessories . . . . . . . . . . . . . . . . . . 20

3 - The Material Strip. . . . . . . • . . • . . . • . . . . . . . . . . . . 42 4 - The Blank . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . 52 5 -

Fourteen Steps to Design a Die . . . . . . . . . • . . . . . . • . 59

6 - How to Lay Out a Scrap Strip . • . . . . . . . . . . • • . . . . . 74 7 - How to Design Die Blocks . • . . • • . . • . . . • . . • . . • . . 90 8 - How to Design Blanking Punches ••.....••..•..••. 102 9 - How to Design Piercing Punches . . . . . . .. . . . . . . . . . 111 10 - How to Design Punch Plates . . . . . . . . . . . . . . . . . . . . 119 11 - How to Design Pilots • . . • . . . • . . . • . . . . . • . . . . . . 125 12 - How to Design Gages • ..• .. . . .. ... .. .. . . . . . . . 135 13 - How to Design Finger Stops . . . . . . .. . ... . . .. .... 142 14 - How to Design Automatic Stops ... . . . . . . . . . . . . . . . 150 15 - How to Design Strippers . . . . . . . . . . . . . . . . ... . .. . 159 16 - How to Apply Fasteners ... ... . . . . . .. . . . . . . . . . . 173 17 - How to Select a Die Set .. .... ..... . . . . . . . . . ... 188 18 -

Dimensions and Notes .•. .... •. ..• ... •...•. . .. 207

19 - The Bill of Material . . • . • . . . . • . . . . . •. .....••. 228 20 - Types of Dies ..• ... . . . . . . . . . .• ...•. ... .. .. 237 Index . • , . ....•. .•. . . . . . • . . . • . . •... .•.... 251

Section 1

INTRODUCTION TO DIE DESIGN Die design, a large division of tool engineering, is a complex, fascinating subject. It is by far the most exacting of all the areas of the general field of tool designing. The die designer originates · designs of dies employed to stamp and form parts from sheet metal, assemble parts together, and perform a variety of other operations.

1-1. BLUEPRINTS After a die has been designed on tracing paper, blueprints or ozalid prints are produced for use in the die shop where the dies are actually bnilt by die

Fig. 1·1. A typical blue print.

makers. This is how a blueprint of a die drawing appears. From such prints die makers build the die exactly as the desi gner has ciesigned it. The drawing must be complete with all required views, dimensions, notes, and specifications. If the die maker is obliged to ask numerous questions a poor job of drawing was done. Good die designers have no trouble in finding employment for their talents. They are always in short supply because the pressed metal industry with which they are associated is a dynamic, rapidly expanding field.

will find stampings. Many are worn on your own person; the ring on your finger is probably a stamping. Most of the parts in your wrist watch are stampings, including the case. Your belt buckle, the metal grommets through which your shoe laces pass, eyeglass frame, fountain pen clip, zipper; all these are stampings. There are even small stamped washers imbedded in the heels of your shoes against which the heel nails bear. Look around the room, any room , and you will find products of the pressed metal industry. Most of the parts in the lighting fixture are stampings; so are threaded portions of light bulbs, door knobs, radiator covers, ash trays; the list is a long one indeed! In the home we find stampings by the score: Pots and pans, knives, forks, and spoons, coffee pot, canister set, pie plates and muffin pans, cabinet handles, kettle, can opener, etc. The refrigerator is almost entirely made of stampings. So are the stove, toaster, and other appliances. And each single part in all these requires an average of from three to six dies to produce it. Every automobile contains hundreds of stampings. The largest is the top, then come the fenders, doors, and wheels. There are hundreds of smaller parts, many of which are covered and seldom seen. For example, the points alone require two very complex dies with thirteen stations each, costing thousands of dollars to build, in addition to assembly dies for fastening the components together. Office machines provide another big stamping field. Typewriters contain hundreds of stampings. So do adding machines, calculators, and dictating machines. I could go on and on because the list is almost endless. Radio and television components require thousands of dies. So do streamlined trains, aircraft, and missiles. All of these are improved from year to year, so an enormous number of new dies are constantly required. The foregoing should give you some idea of the great size and importance of the pressed metal industry. Stampings engineering has grown in the last thirty years into a vast field, one filled with opportunity for the alert.

STAMPINGS

1-2. SCRAP STRIP

Stampings are parts cut and formed from sheet materiaL Look around you! Wherever you may be, there you

Shown here is the scrap strip and finished Injectors for Schick razors. These parts are cut and formed in a

2

INTRODUCTIO

TO DIE DESIGN

nine station progressive die. Once the strip has been started through the die, a complete injector is produced with each stroke of the press. This layout illustrates perfectly how complex, accurate stampings can be produced in large quantities when operations are carefull y planned and die s are properly designed.

Fig. 1·2. An injec tor lor a razor (at left) ond scrap strip from which it wos cut.

DIE DESIGN How then shall we enter into the study of die design? Obvious! y, we shall have to begin cautious! y, learnin g each principle thoroughly before proceeding to the next one. Otherwise it is quite likely that we should soon become hopelessly involved in the complexities of the subject and in the bewildering number and variety of principles which must be understood. Wh at, then, is a die? The •10rd "die" is a very general one and it may be well to define its meaning as it will be employed in our work. It is used in two distinct ways. When employed in a general sense, it means an entire press tool with all components taken together. When used in a more limited manner, it refers to that component wh ich is machined to receive the blank, as differentiated from the component called the punch which is its opposite member. The distinction will become clear as you proceed with the studies. In this introduction you are to learn the names of various die components and to get some idea of how they go together and are operated. In addition, we will consider the steps taken in designing, building, and inspecting a die in a representative press shop. Finally, operations which are performed in dies will be listed and illustrated. In other sections of the book, the design of dies and die components will be explained in a fa r more thorough manner so that your understanding will be complete in every respect .

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Fig. 1·3. A typi col punch pr es s.

by several manufacturers and they may be purchased in a great variety of shapes and sizes. Punch shank A is clamped in the ram of the press. In operation, the upper part of the die set B, called the punch holder, moves up and down with the ram. Bushings C, pressed into the punch holder, slide on guide posts D to maintain precise alignment of cutting members of the die. The die holder E is clamped to the bolster plate of the press by bolts passing through slots F. In Section 17, "How to Select a Die Set," all types of die sets will be described and illustrated, and rules will be given to help you determine the correct type to employ under specific conditions.

1-3. PUNCH PRESS This is a photograph of a typical punch press in which dies are operated to produce stampings. The bois er plate A is a thick steel plate fas tened to the press frame. The com plete die is clamped securely on this bolster plate. The upper portion of the die is cl amped in ram B which is reciprocated up and down by a crank. As the material strip is run through the die, the upper punches, fastened to the moving ram of the press, remove blanks from it. The subject of punch presses will be covered in detail in Section 2, ''Presses and Press Accessories" .

1-4. Dl E SET This is called a die set, and all parts comprising the die assembly are built wi thin it. Die sets are made

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Fi g. 1·4. A lypi col die set.

3

INTRODUCTION TO DIE DESIGN

1-5. PART DRAWING To begin our study of the various components which make up a complete die , let us consider the drawing of the link illustrated here. This part is to be blanked from steel strip and a die is to be designed for producing it in quantity. The first step in des igning any die is to make a careful study of the part print because the information given on it provides many clues for solving the design problem.

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1-7. DIE DRAWING (See page .4) This is a complete die drawing ready to be printed in blueprint form. To the uninitiated , it mi ght appear to be just a confusing maze of lines. Actually, however, each line represents some important information wh ich the die maker must have to build the die successfull y. In illustrations to follow, we will remove the individual parts from this assembly and see how they appear both as three or two view drawings and as pictorial views to help you to visualize their shapes. As you study further, keep coming back to this illustration to see how each component fits in. When you get through, you should have a good idea of how the various parts go together to make up a complete die.

1-8. Dl E ASSEMBLY

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defect is important enou gh for the method to be discarded and, instead, the blanks will be positioned the long way in the strip as shown at B. The grain will then occur along the length of each blank for maximum stiffness and strength.

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This is a pictorial view of the entire die shown in Fig. 1-7. The die pierces two holes at the first station, and then the part is blanked out at the second station. The material from which the blanks are removed is a cold-rolled steel strip. Cold-rolled steel is a smooth, medium-hard steel, and it gets its name fro m the process by which it is produced. It is rolled, cold, between rollers under high pressure to provide a smooth surface. The strip A is shown entering the die at the right.

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Fig. l-5. A typical part drawing.

1-6. SCRAP STRIP Next, a scrap strip would be designed as a guide for laying out the views of the actual die. This illustration shows the material strip as it will appear after holes have been pierced and the blank has been removed from it. We would first consider running the blank the wide way as shown at A. When blanks are positioned in this manner, the widest possible strip is employed and more blanks can be removed from each length of strip. In addition, the distance between blanks is short and little time is consumed in moving the strip from station to station. However, for this particular blank there occurs a serious disadvantage in this method of positioning. Since the grain in a metal strip runs along its len gth, the grain in each blank would run across the short width and the blanks would be weak and lacking in rigidity. This

Fig. l-8. A picto rial view of an ent ire die.

1-9. Dl E PARTS

A

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Fig. 1·6. Typical scrap str ip layouts.

This is an exploded drawing of the die shown in Fig. 1-8. Following are listed the names of the various die components. These part names must be memorized because we shall keep referring to them many times in future work. A. Punch holder of die set B. Piercing punch C. Pilot nut D. Square head set screw

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L. Back gage M. Front spacer N. Die block 0. Die holder of die set. Taken together, Figs. 1-8 and 1-9 show the operation of a representative "pierce and blank" die. The strip is advanced until it contacts the toe of the finger stop K, which has been moved forward by the operator. The press is tripped and the piercing punches B pierce two holes in the strip end. The finger stop is then retracted and the strip is advanced until it contacts the toe of automatic stop J, Tripping the press again causes two holes to be pierced in the strip at the first station, while at the second station blanking punch F removes a blank from the strip and pushes it into the corresponding opening in die block N. The acorn shaped pilots H engage the previously pierced holes to register the strip correctly before cutting occurs.

1-10. THE SCRAP STRIP Three views of the material strip are shown here exactly as they appear in the die drawing in Fig. 1-7. In addition, a pictorial view is applied at the upper right corner to help in visualizing the strip in your mind. In other words, this is the way you would imagine the strip in order to draw it in three views. The top or plan view shows the strip outline as well as all openings. This would be made actual size on the drawing. The holes are represented by circles at the first station, and the blanked opening is shown at the second station. At the lower left, a side view of the strip is

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Fig. 1·9. An exploded view of the die shown in Fig. 1·8.

E. Jam nut F. Blanking punch

G. Punch plate .

drawn. It is shown exactly as it would appear at the bottom of the press stroke, with the pierced slugs pushed out of the strip at the first station and the blank pushed out of the strip at the second station. The narrow end-view at the lower right corner is shown as a section through the blanking station, and the blank is shown pushed out of the strip. The strip in many instances is drawn shaded to differentiate it from the numerous lines which will represent die members, In the upper plan view, shading lines would appear on the surface of the metal. In the two lower views, the lines are shown in solid black to further differentiate the strip from the die members.

H. Pilot

I . Stripper plate J. Automatic stop K. Finger stop

1-11. THE DIE BLOCK The die block is made of hardened tool steel into which holes have been machined, before hardening, at


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the piercing station and also at the blanking station. These are the same size and shape as the blank holes

drawing, Fig. 1-7, to improve your ability to read a die drawing.

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Fig. 1-11. The die block.

and contour. Other holes are tapped holes used to fasten the die block to the die holder, and reamed holes into which dowels are pressed to fix its location relative to other die parts. The top view is a plan view of the die block. The lower left view is a section through the holes machined for piercing and blanking. Lines drawn at a 45 degree angle, called section lines, indicate that the die block has been cut through the center, the lines representing the cut portion. Similarly, the end view is a section cut through the die block at the blanking station. A tapped hole is shown at the left and a reamed hole at the right side. These are for the screws and dowels which hold the die block to other die components. Sectioning a die, that is, showing the die as if portions were cut away to reveal the inside contours of die openings is a very common practice. In fact, practically all dies are sectioned in this manner, The die maker can then "read" the drawing far more easily than if outside views only were shown because they would contain many dotted, or hidden lines. Always remember that all .drafting is, in a sense, a language. A die drawing is a sort of shorthand which is used to convey a great deal of information to the die maker. Anything which can be done to make it easier for him to read the drawing will save considerable time in the shop. Now refer back to Fi g. 1-7 and see how easily you can pick out the three views of the die block. That is exactly what the die maker would have to do in order to make the die block.

Fig. 1-12. The blanking punch.

1-13. PIERCING PUNCHES Piercing punches pierce holes through the material strip or blank. They are usually round and are provided with a shoulder to retain them in the punch plate. When a piercing punch penetrates the strip, the mat erial clings very tightly around it and means must be provided to strip, or remove this material from around the punches. Whatever is employed to remove such material is called a stripper.

-fF-3E-+ Fig. 1-13. A piercing punch.

1-14. PUNCH PLATES 1-12. THE BLANKING PUNCH These are the three views of the blanking punch which removes the blank from the strip. Its lower portion is made the shape and size of the required blank. A flange at the top provides metal for fastening the blanking punch to the punch holder of the die set with screws and dowels. Two holes are reamed all the way through the blanking punch for retaining the pilots which locate the strip prior to the blanking operation. Locate the views of the blanking punch in the die

The punch plate is a block of machine steel which retains punches with their heads against the punch holder of the die set. The punches are held in counter· bored holes into which they are pressed. Four screws and two dowels retain the punch plate to the punch holder of the die set. The screws prevent it from being pulled away from the punch holder. Dowels, which are accurately ground round pins, are pressed through both the punch plate and punch holder to prevent shifting. Locate the front view and plan view of the punch plate in the die drawing, Fig. 1-7.


7

1-17. FINGER STOPS The finger stop locates the strip at the first station. In progressive dies having a number of stations, a finger stop may be applied at each station to register the · strip before its contact with the automatic stop. Finger stops have slots machined in their lower surfaces to limit stop travel. Section 13, "How to Design Finger Stops," will show a number of ways in which these components are applied.

Fig. 1·14. A punch plate.

1-15. PILOTS Pilots are provided with acorn shaped heads which enter previously pierced holes in the strip. The acorn shape causes the strip to shift to correct register before blanking occurs. Section 11, "How to Design Pilots", will show many different ways of applying these components.

Fig. 1·17. A finger stop,

1-18. AUTOMATIC STOPS Automatic stops locate the strip automatically while it is fed through the die. The operator simply keeps the strip pushed against the automatic stop toe, and the strip is stopped while the blank and pierced slugs are removed from it, then automatically allowed to move

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1-16. THE BACK GAGE The back gage is a relatively thin steel member against which the material strip is held by the operator in its travel through the die. The front spacer is a shorter component of the same thickness. The strip is fed from right to left. It rests on the die block and is guided between the back gage and front spacer. The distance between the back gage and front spacer is greater than strip width to allow for possible slight variations in width.

Fig. 1·18. An automatic stop.

one station further and stopped again for the next cutting operation. There are many ways of applying automatic stops, and these will be discussed and illustrated in Section 14, "How to Design Automatic Stops."

1-19. THE STRIPPER PLATE Fig. 1·16. The back gage.

The stripper plate removes the material strip from around blanking and piercing punches. There are two types: spring-operated stripper plates, and solid strip-

INTRODU CTION TO DIE DESIGN

8

per plates, like the one illustrated. The stripper plate has a slot A machined into it in which the automatic stop operates. Another slot B at the right provides a shelf for easy insertion of a new strip when it is started through the die ,

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more clearly. The upper left view is a plan view of the lower die holder with the punch holder removed from it. The punch holder is shown at the upper right, and it is drawn inverted, or turned over, much like an opened book. In the die drawing, Fig. 1-7 then, all punches are drawn with solid lines. Were the punch holder not inverted, most lines representing punches would be hidden and the drawing would contain a confusing maze of dotted lines. Another reason for inverting the punch holder is that this is actually the position assumed by the die holder and punch holder on the bench as the die maker assembles the die, and it is easier for him to read the drawing when the views have been 'drawn in the same position as the die on which he performs assembly motions.

1-22. DIMENSIONS AND NOTES Fig. 1·19. The stripper plate,

1-20. FASTENERS Fasteners hold the various components of the die together. This illustration shows the commonly used socket cap screw. These fasteners are available from various suppliers, and all have a threaded portion and a larger round head provided with an internal hexagon for wrenching. All fasteners employed in dies will be discussed in Section 16, "How to Apply Fasteners," and rules will be given for specifying the correct types under given conditions. As you have been doing for previous illustrations, pick out the fasteners shown in the die drawing, Fig. 1-7. Note that in section views, screws are shown on one side and dowels on the other.

With the die design completed, all dimensions and notes are applied to the drawing. This is the die set note which tells the die maker exactly what die set to order and which gives required information about punch shank diameter, type of guide bushings, and diameter and length of guide posts.

CD DANLY DIE SET CAT. NO. 0603-AI 11J2 DIA. PUNCH SHANK STEEL SHL' D. BUSH. 11 1 DIA. X 5 GUIDE POSTS

Fig. 1·22. A typical die set note.

1-23. BILL OF MATERIAL The bill of material is filled in last. This gives required information and specifications for ordering standard parts and for cutting steel to correct dimensions. This material is cut and assembled in the stock room and placed in a pan, along with a print of the die drawing. When filled, the pan must contain everything the die maker will require for building the die, including all fasteners and the die set.

PROCESSING A DIE Let us now consider the steps taken in designi ng, building, and inspecting a representative die. At b1e same time, you will gain an insight into the operation of press shops, tool-rooms, and manufacturing plants so that your understanding of tool and manufacturing processes will better than a casual one.

The Product Fig. 1-Xl. Socket head cop screw for use as a fastener.

1-21. THE DIE SET The die set is drawn with four views. At the lower left is shown a section through the entire die set. The side view, lower right, is a section view also, with a portion of the die set cut away to show internal holes

First, we will consider the product to be manufactured. The product engineering department designs the product. In most plants, the work consists in improving the product from year to year to meet changing styles and changing requirements of customers. After management has decided upon the final form of the new or improved product, a directive is sent to the process planning department to route the various


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parts through the appropriate manufacturing departments. The process or methods engineers then plan the order of manufacturing operations and decide what will be used. They request that the tool design department produce designs of all jigs, fixtures, cutting tools, and dies needed for efficient production of the parts.

The Part The part which is to be machined, formed, pressed, or inspected is called by one of three names: 1. Part 2. Work 3. Workpiece Part is the preferred term, but workpiece or simply, work, are often employed as alternate names and all th ree terms will be used throughout this book. The print on which this part, work, or workpiece is represented is called a Part Print. It may be a blueprint, or quite often it is a blue and white ozalid print. Therefore, in designing a die for producing a stamping, e die designer works from a part print.

Processing Following is the sequence of operations or procedure followed in processing a stamping through the planning stages. Substantially the same series of steps would be taken in any large or medium-size manufacturing plant. After a product designer had prepared layouts and assembly drawings of the product to be manufactured, the engineering department would prepare detail drawings of each individual component which the shop would have to produce. These contain all required views, dimensions, and explanatory notes to represent all detail features of the objects. Prints of these detail drawings are sent to the process planning or processing department. When stamp ings are required, it is the function of the men of this department to determine how the stampings are to be made. They decide how many operations will be required and what presses will be employed to make them . This department thus assumes the responsibility of determining the sequence of manufacturing opera-


10 tions. The information is noted on a form called a route sheet.

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Yex3f4x4% i"a x 16 x 'l's

STD..

o/eDJA. x I ~4

1'8DIA.X

z

soc AP DOWEL

2

DOWEL

STD.

1

JAM NUT

STD.

SQ. HD. SET SCR. STD.

20

1 2.

DOWEL

510.

19

4

SOC. CAP SCR..

STD.

7'8 -16 x

STD.

7"8 DJA. x I Y2.

1 8 2. 17 4 16 15

2 1

14 13

1

SCR

DOWEL

SOC. CAP. SCR. STD.

2.

1 11 1

12

-

!:JJ2

%- 16 X I y2.

RIVET

C.R.S.

STRIP REST BACK GAGE

C.R.S. T.S.

y4

fa

- 20

~-20X lo/4

I Y4

%DIA.X

rs

1'e-16xl Ya DIA. x 3fA

YRx%x1Yc. Ys x 1'4 x8Ya o/4 DIA.x I Vs

PIERCE PUNCH T.S. PUNCH PLATE M.S.

1x2x2Va

BLANK-PUNCH T. S.

1Yz.x2x2~

10

1

STRIPPER

C.R.S.

o/a x 2}'zX4%

9

1

Dl E BLOCk:

T.S.

8

1 1

DOWEL

STD.

1}4 X 2J4x 4% ¥i6 X DIA,X Yz.

Fl NGEQ STOP

T. S.

Ys x o/s x 21's

SOC. CAP SCR. STD. SPRING s.w.

110-24

5

1 1

4

1

SPRING PIN

C.R.S.

t4DIA.X 2 o/a

3 2

1

HINGE PIN

D.R.

YaDIA. X

1 1

AUTO STOP

T. S.

V4 xyzx 2Y4

OlE SET

PUR,

SEE NOTE.

MAT.

SPECIFICATIONS

7 6

1

DET, REQ'D

PART

NAME

x Y4

TO SUIT

1/8


·t

ASSEMBLY 2SrA. 'P.S. D. TYPE 40-BL FOR- 11 HOP'PE'R LINK" DRAWN BY J. R.'P . CUSTOMER TELECHRON DATE APR. 25 1961 ORDER 49268 CHECKED BY C. H. H. DATE 4-27-61 APPROVED BY R.S . DATE 4 28-bl SCALE.· FULL

SHEET I OF 2 AIB .I C I D I E I F

I j l

1•1

DRG. NO. 0-1000

they contain will vary. However, the following are usually included: 1. The Heading. This is located at the top of the sheet and it contains the following information: Part name Part number Drawing number Number of parts required Name of product engineer Date. In addition, the product name and model number may be included 2. The number of each operation required to make and inspect the part. Numbers are most frequently listed in increments of 5, as 5, 10, 15, 20, etc., to provide numbers in sequence for additional operations which may be found necessary in manufacture or when changes are made in the design of the product 3. The name of each operation 4. The name and numberof the machine in which the operation is to be performed 5. Estimates of the number of parts which will be completed per hour for every operation. These estimates are altered after production rates have been measured accurately by the time study department. Route sheets are supplied to the following departments: Tool design department Production department Inspection department. Of course, any machine or product will contain many components which have been standardized and which can be purchased from outside suppliers or vendors. Such items would include screws and dowels, bearings, clutches, motors, and many more. The purchasing department would be supplied with a bill of material, and purchase orders would be issued for all parts to be bought.

1-25. TOOL OPERATION SHEET The tool operation sheet is prepared from the route sheet and it usually lists the following: 1. Number of each operation 2. Name of each operation 3. Machine data 4. List of all standard and special tools required for the job 5. Names and numbers of all special tools which are to be designed and built. These numbers are marked on tool drawings and later stamped or marked on the actual tools for identification. Tool operation sheets are helpful in planning and developing a tooling program. Copies go to the tool des igners and to the tool purchasing department. Before proceeding further, study carefully the tool operation sheet illustrated.

Fig. 1·23. A typical bill of material.

1-26. DESIGN ORDER 1-24. ROUTE SHEETS Route sheets are designed to suit the requirements of the individual plant and therefore the information

The design order is a slip of paper authorizing work on an actual design. One is written for each die or special tool required and the information is taken from the route sheet. In addition, it may give instructions

11



ROUTE PART NAME PART NO.

Ho!!_S_l.J'lg Cover

_~!)_2 6_§ ____

_

NO. OF PARTS DRG. NO ..

SHEET

800,000 - !_2_2~ -.

Oct. l'L l9~L

DATE

-

PROD. ENG.

J. Cochran - · - -·--

SHEET NO. _ ],__ __ OF _ ],_ OPER NO.

5

OPERAT I O N

Shear Sheet into strips

MACHINe

Bliss

30

,0001

~r_!rlg_ - - -- ·--·-

Shears -- - - - No. 37 (Shop)_

(HOU RS )

--

-- : _

-- - - -- - - - -- --

--·--·--

---

SET UP

TIME (HOURS)

DEPT.

-·--

- - - - -- ----- - -

10

Blank

Federal Press No. 33 No.442 (Shop)

25

.0001

---

15

Form

Federal Press No , 44 No. 337 (Shop)

25

.0002

---

20

Wash and sh1o t o stores

Truck

Fig. 1·24. A typical route sheet.

regarding the type of die preferred. Following is a list of the information usually given on a design order. 1. Department name 2. Tool name 3. Date 4. Tool number 5. Part name 6. Part number 7. Operation 8. Machine in which tool. is to be used 9. Department in which machine is located 10. Number of parts to be made.

TOOL INSPECTION DEPARTMENT After a die has been designed, a set of prints is sent to the tool inspection department. After the die has been built they will inspect it to make certain that it was constructed to specifications given in the tool print. When the die is built by an outside tool shop, it is inspected by the tool inspection department upon de-

livery and the same inspection procedures are followed to determine if stampings produced by it are held to tolerances specified on the part print.

PRODUCTION After the tool inspection department has approved its construction and accuracy, the die is delivered to the department where it will be used. The set-up man for that department installs it in the press where it will be operated and he produces a few parts under the same conditions in which the die will run in actual production. These parts are taken to the production inspection department. There, they are inspected to determine whether or not sizes have been held to tolerances specified on the part print. After the production inspection department has determined that the samples are satisfactory, a form is issued and signed by the chief inspector authorizing production with the die. After the production foreman receives production orders from the production department, he will proceed to go into production of the


12

NAME OF SCHOOL OR COMPANY AND ADDRESS PART NAME PART NO.

Housing Cover 10~68

Operation Number

5

Oot. 20, 1961

DATE

TOOL OPERATION SHEET A,ROVED 1Y OPERATION NAME

TOOL NAME

TOOL NUMBER

J • Coollran

lntlr~·

O.pt.

tiont

No.

Shear Sheet into str1DI

_3_0

EQUIPMENT NAME AND NUMBER

Bl1u Squar!M_ Shears Shop No._11

10

Blank

Blanking _llunoh and d1e

T~Qll

__Qn

2_i

kural Preu No. JJ ShQI>_ No, 442

15

Por11

Forming punoh and d1e

T-1Q1_4

Des

li_

Federal Preu No. 44 Shop No. _111_

20

Wash and sh1p to stores

Truok

Fig. 1-25. A typical tool operation sheet.


DESIGN ORDER NO.

102 TO

Tool Des1£n

DESIGN

Forming Punch and Die

FOR

Forming Lower Flange

De~rtment

Oct. 22. 1961

DATE

PART NAME

Housing Cover

PART NO.

10568

TOOL NO.

T-3074

USED IN .

No. 20 Bliss Press

SHOP NO.

406

DEPARTMENT

Press

NO.

NUMBER OF PARTS REQUIRED COMPLETED

22

800 000 CANCELLED

REASON SIGNED -- ~

Fi g. 1- 26 . A typical design order.


stampings. Production orders 5pecify how many parts are to be run, when they will be required, and where they are to be delivered. After a new die has been in production for a few hours or so and it is found to perform satisfactorily, the order which was issued to the tool-room to build the die is closed and no more time may be charged against it. In this connection it is interesting to note that records are kept of all time devoted to designing, building, inspecting, and trying out the die in order to determine the actual tool cost, illustrating perfectly that "time is money."

DESIGNING THE DIE Before a designer begins to draw, there are a number of things which he must sedously consider. It is now possible to list all the items which will be required before he can begin designing intelligently. They are: 1. The part print 2. The operation sheet, or route sheet 3. The design order 4. A press data sheet. In addition, he may have a reference drawing of a die similar to the one he is to design or a sketch of a proposed design prepared by the chief tool designer or group leader suggesting a possible approach to solution of the problem. Let us consider further the information required:

Part Print. The part drawing gives all necessary dimensions and notes. Any missing dimension must be obtained from the product design department before work can proceed. Operation Sheet. The operation sheet or route sheet must be studied to determine exactly what operations were performed upon the workpiece previously. This is very important. When the views of the stamping are laid out, any cuts which were applied in a previous operation must be shown. The Design Order. This must be studied very carefully because it specifies the type of die to be designed. Consider particularly the operation to be performed, the press in which the die is to be installed, and the number of parts expected to be stamped by the die. The latter will establish the class of die to be designed. The Machine Data Sheet. The die to be designed must fit into a particular press and it is important to know what space is available to receive it and what interferences may be present. In time you will come to realit'le the importance of careful and repeated study of the part print, operation sheet, and design order because there can be no deviation from the specifications given.

DRAWING If the information on a drawing is complete, concise, and presented in the simplest possible manner, the die maker can work to best advantage. The first step in originating plans for a new die is the preparation of a s ketch or sketches of significant features of the proposed die. These will become a guide for beginning the actual full-size layout on tracing paper. However,

13

it is a mistake to spend too much time in this phase of the work or to try to develop the entire design in sketch form because then decisions can become too arbitrary and inflexible. Always keep your mind open to possible improvements as you develop the design in layout form. You will find that, often, the first or second idea sketched out can · be considerably improved by alteration as work progresses. Often the first idea proves entirely impractical and another method of operation must be substituted. Before beginning the sketch, place the part print, operation sheet, and design order before you on the drawing table. The three must be studied together so that a complete and exact understanding of the problem will be realized. This study will form the basis for the creation of a mental picture of a tool suitable for performing the operations - one which will meet every requirement. The sketch you make may be a very simple one for simple operations or it may be more elaborate . In fact, a number of sketches may be required for more complex operations and intricate designs. In any event, the sketch will clarify your ideas before a formal layout is attempted. In addition, it will form the basis for a realistic estimate of the size of the finished die so that you may select the proper sheet size for the layout.

LAYOUT Laying out the die consists of drawing all views necessary for showing every component in its actual position. In the layout stage, no dimensions are applied and neither is the bill of material nor the record strip filled out. After the die has been laid out, the steps necessary for completing the set of working drawings are more or less routine. A properly prepared assembly drawin g contains six general features: 1. All views required for showing the contour of every component including the workpiece 2. All assembly dimensi ons. These are dimensions which will be required for assembling the parts and those for machining operaf ms to be performed after assembly 3. All explanatory notes 4. Finish marks and grind marks to indicate those surfaces to be machined after assembly 5. A bill of material listing sizes, purchased components, materials, and number required for all parts 6. A title block and record strip with identifying information noted properly.

DETAIL DRAWINGS After the assembly drawing has been completed, detail drawings are prepared unless all dimensions were placed on the assembly, as is done for simple dies. Detail drawings are drawings of individual components and they contain all dimensions , notes, and supplementary information so that each part can be made without reference to the assembly drawing or to other detail drawings. Such information usually includes ten distinct elements : 1. All views required for identifying every detail of the part must be drawn 2. Every dimension needed for making the part must be given


14

3. Suitable notes for furnishing supplementary in4. 5. 6.

7. 8.

9. 100

formation which dimensions do not cover must be applied Finished surfaces must be identified The name of the part and its number must be given The material it is to be made from must be specified The number required per assembly must be stated The scale to which the drawing has been laid out must be listed The draftsman's name or initials must be signed The date must be specified.

CHECKING After a set of drawings has been completed and the designer has reviewed them for possible omissions or errors, they are turned over to the group leader who will bring them to the checker to be checked. Accompanying them will be the design order, part print, and any notes or sketches which may have accompanied them when the designer received the job. The checker will require all these in order to do his work properly. The checker will first study the operation of the die to make sure that it will function properly and that its cost will not be excessive for the work it is to perform. After he is satisfied that it has been designed properly, he will check every dimension, note, and specification for accuracy. ·He usually works from a check print. This is a blue and white print having blue lines and a white background. With a yellow crayon, he will cover with yellow color every dimension he finds to be accurate, and with a red crayon he will cover with red color every dimension he finds to be wrong. Above or to the side he will write the correct dimension in red. The tracings, along with the check prints, are then returned to the designer for correction. Incorrect dimensions are carefully erased to remove all graphite from the paper. An erasing shield is ordinarily used to prevent smudging of other dimensions or lines. Correct dimensions are then lettered in place. After the tracings have been corrected, they are returned to the checker and he checks the job again to make sure that no correction was overlooked. He then signs the drawing in the space provided and enters the date the drawing was checked. After drawings have been completed and checked, they must be ap proved by the chief designer, chief tool engineer, or possibly the plant superintendent and others who are held responsible by the management for the cost and quality of dies used in the plant. Usually, these approvals are routine after drawings have been approved by the checker. However, it may sometimes happen that someone will refuse to sign because he may feel that the die will not work as well as expected, will not deliver the number of parts required per day, will be too expensive to lmild, or for some other reason. If he convinces the others that his objections are valid, the drawings will have to be altered or a new design begun, depending upon the extent of the changes to be made. 0

PRINTS After approval, blueprints or ozalid prints are made from the tracings, or originals. A small print is taken of the bill of material only. This is sent to the stock cutting department where steel is stored and cut as required. The stock cutter goes over the list, selects bars of proper thickness and width, or diameter, and saws them to the lengths specified for each item listed. These cut blocks and plates are placed in a pan, along with screws, dowels, and other parts which are kept in stock. When purchased components are delivered to the plant, they are also placed in the pan. Finally, the pan contains a set of die prints and a part print and it is delivered to the tool-roam where the tool-roam foreman turns it over to the die maker who will build the die. One of the prints is sent to the purchasing department. There, orders are written to authorize purchase of all components which will enter into building the die. If the entire die is to be built by an outside tool shop, a purchase order is sent to them. If it is to be built within the plant, an order authorizing construction is sent to the tool-room. In addition, requisitions are made out for the following: 1. Standard parts or assemblies which are not kept in stock and which must be purchased 2. Castings, forgings, or weldments required for construction of the die 3. Steels of special analysis not carried in stock 4. Special sizes of steels or other materials not stocked. °

The purchasing agent must plan for delivery of all these components before the date set for beginning construction of the die. File cards are then made out for the drawings and they are filed away in drawing files. These are usually kept in the tool and die design department, although some plants keep them in a vault. The file cards list the job by name and numb.er, and they contain the number of the drawing file in which drawings are kept to help in locating them if required again in the future.

1-27. CHECKING A SCRAP STRIP A die maker examines a scrap strip and finished stamping. This part was produced in a multiple station progressive die in which the operations are done progressively from station to station and a finished part is delivered with every stroke of the press.

1-28. PROGRESSIVE DIE These are photographs of the upper (top) and lower (bottom) sections of the die used to produce the scrap strip and stamping shown in Fig. 1-27. The design of progressive dies requires a thorough knowledge of die principles. A designer capable of designing progressive dies is considered one of the top men in the field.

DIE OPERATIONS Just exactly what operations are performed in dies? This question is asked often and I have prepared the following illustrated list of the twenty types of operations which are performed in dies:


15

Bethlehem Steel Co.

Fig. 1·27. Examining a scrap strip.

1-29. BLANKING Stampings having an irregular contour must be blanked from the strip. Piercing, embossing, and various other operations may be performed on the strip prio r to the blanking station. Bethlehem Steel Co.

-30. CUT OFF Cut-off ope~ations are those in which strip of suitable width is cut to length. Preliminary operations beore cutting off include piercing, notching, and emboss. g. Although they are relatively simple, many parts can be produced by cut off dies .

Fig. 1·28. The upper (top) and the lower (bottom) portions of a typical progressive die.

'-31. COMPOUND Compound dies pierce and blank simultaneously at e same station. They a re more expensive to build and • ey are used where considerable accuracy is required in the part.

1-32. TRIMMING When cups and shells are drawn from flat sheet etal the edge is left wavy and irregular, due to une\·en flow of metal. This irregular edge is trimmed in a · mi ng die. Shown is a flanged shell, as well as the · ri mmed ring removed from around the edge.

Fig. 1·29. A blank and the st rip fr om which it has been cut.

1-33. PIERCING Piercing dies pierce holes in previously blanked, 'ormed, or drawn parts. It is often impractical to pierce oles while forming or before forming because they ould become distorted in the forming ope ra tion. In s uch cases they are pierced in a piercing die after orming.

Fig. 1-30. Part separated from strip in cut·off operation.

INTRODUCTION TO DIE DESIG '

16

Fig. 1·31. Thi s port is blan ked and pierced simu ltaneous ly in a com· pound die.

Fig. 1-34. The result of shov ing in a shavi ng die.

Fig. 1·35. Serrations app lied in a broaching die. Fig. 1·32. The result of trimming in a tr imming die.

Fig. 1·36 . Th e seam on this port is done as a secondary operati on in a ho rn di e.

Fig. 1·33. Holes pierced in a previously drown part.

1-34. SHAVING Shaving consists in removing a chip from around the edges of a previously blanked stamping. A straight, smooth edge is provided and therefore shaving is frequently performed on instrument parts, watch and clock parts, and the li ke. Shaving is accomplished in shaving dies es pecially designed fo r the purpose.

1-35. BROACHING This illustration s hows serrations applied in the edges of a sta mping. These would be broached in a broaching die . Broaching operations are similar to shaving operations. A se ries of teeth removes the metal instead of just one tooth as in shavin g. Broaching must be used when more material is to be removed than could effectively be done with one tooth.

1-36. HORNING Horn dies are provided with an a rbor or horn over wh ich the parts are placed for secondary operations such as seaming, as illustrated. Horn dies may also be used for piercing holes in the sides of shells.

J-37. SIDE CAM OPERATIONS Piercing a number of holes simultaneously arou nd a shell is done in a side cam die. Side cams convert the up-and-down motion of the press ram into horizontal or angular motion when it is required in the nature of the work.

J-38. BENDING Bending dies apply simple bends to stampings. A simple bend is one in which the line of bend is straight. One or more bends may be involved, and bending dies are a large and important class of press tool.

17

I TRODUCTION TO DIE DESIO

Fi g. 1·37. The holes are pierced simultaneously in a side com die.

Fig. 1·40. Shell drown from a flat sheet.

Fig. 1·38. Stomping bent in a bending di e.

Fig. 1·39. Stom ping formed in a forming die.

1-39. FORMING Forming dies apply more complex fonns to workpieces . The line of bend is curved instead of straight and the metal is s ubjected to plastic flow or deformation.

1-40. DRAWING

Fig. 1·41. Lip on thi s drawn she ll prod uced in curling die.

would be a hinge in which both members are curled to provide a hole for the hinge pin.

1-42. BULGING Bulging dies expand the bottoms of previously drawn shells. The bulged bottoms of some types of coffee pots are formed in bulging dies .

Drawing dies transform flat sheets of metal into cups, shells, or other drawn shapes by subjecting the material to severe plastic defonnation. Shown in the illustration, a rather deep shell has been drawn from a flat sheet.

In swaging operations , drawn shells or tubes are re· duced in diameter for a portion of their lengths. The operation is als o called neckin g.

1-41. CURLING

1-44. EXTRUDING

Curling dies curl the edges of drawn shells to provide strength and rigidity. The curl may be applied over a wire ring for increased strength. You may have s een the tops of sheet metal pails curled in this manner. Flat parts may be curled also. A good example

Extruding dies cause metal to be extruded or squeezed out, much as toothpaste is extruded fro m its tube when pressure is applied. This shows a collapsible tube formed and extruded from a solid slug of metal.

1-43. SWAGING

18


1-45. COLD FORMING In cold forming operations, metal is subjected to high pressure and caused to flow into a predetermined form . In coining, the metal is caused to flow into the shape of the die cavity. Coins such as nickels, dimes, and quarters are produced in coining dies.

Fig. 1·42. Bulge in this drawn shell produced in bulging die.

Fig. 1·45. Cold-formed part in which metal flow is caused by high pressure.

1-46. PROGRESSIVE OPERATIONS Progressive operations are those in which progressive dies perform work at a number of stations simultaneously. A complete part is cut off, at the final station, with each stroke of the press. The die shown in Fig. 1-28 is a progressive die. Fig. 1·43. Drown shell that has been swaged.

Fig. 1·46. Part and strip produced in a progressive die.

1-47. SUB PRESS OPERATIONS Sub press dies are used for producing tiny watch, clock, and instrument components, represented by the watch needles shown. Sub presses are special types of die sets used only for such precision work.

Fig . 1·44. Drawn shell that has been extruded.

Fig. 1·47. Typical precision parts produced in sub press dies.


1-48. ASSEMBLY Dl ES Represented is an assembly operation in which two studs are riveted at the ends of a link. Assembly dies

Fig. 1·48. Part produced in an assembly die.

19

assemble parts with 'great speed and they are being used more and more. From the foregoing, you can perhaps appreciate what a wide field die design engineering really covers. You must have come to realize that it is indeed a pleasant and interesting occupation, one which will stimulate your mind in much the same manner as working out fascinating puzzles. In addition, you will come to find that is a very profitable one. As you study the sections to follow, you will be introduced, step by step, to the fundamental die components and you will learn the methods by which die designers assemble these components in designing dies. When you have completed the book you will know the elements of die design quite thoroughly. Knowledge such as this is well paid for by Industry. You will have acquired the foundation of a career that can benefit you for the rest of your life.

Section 2

PRESSES AND PRESS ACCESSORIES PRESS POWER

Before undertaking the study of die design, it will be necessary to learn the construction and operation of the punch press and about the many types of presses in which dies are operated. Learning die design will be more simply and easily accomplished then because you will understand the relationship between the tool, that is the die with its various components, and the drive, that is the press which operates the die to produce stampings. In this section you will also learn about the various accessories employed in conjunction with presses in order to make up complete press lines.

There are four sources of power for operating presses:

1. Manual - such presses are hand-operated or footoperated 2. Mechanical - These presses are motor driven and they may have a flywheel, single reduction gear, or multiple reduction gear 3. Hydraulic - These may be oil-operated or wateroperated. 4. Pneumatic - Such presses are operated by compressed air.

PRESS TYPES PRESS SPEED

There are five basic types of presses in which dies are operated. They are: 1. Gap-Frame Presses 2. Straight-Sided Presses 3. Four-Post Presses 4. Underdrive Presses S. Super High Speed Presses.

When cutting dies are operated, press speeds range from 40 to 800 strokes per minute, usually. Drawing and forming dies must be run more slowly to allow time for the metal to flow. Speeds range from 5 to 100 strokes per minute, depending on part size and severity of the operation performed.

Each type, in turn, contains a number of sub-types in a bewildering variety of sizes and shapes.

2-1. GAP-FRAME PRESSES Gap-frame presses are the most widely used type. They produce many thousands of different kinds of parts ranging from small instrument components to large appliance and automotive parts. Operations performed include blanking, trimming, bending, forming and drawing of cups and shells. The distinguishing charac· teristic of a gap-frame press is its open throat. The

PRESS CONSTRUCTION Presses are manufactured by two methods of construction: Cast construction and welded construction. Smaller presses are usually cast. Large presses may be cast or they may be made of welded steel.

20

21

PRESSES AND PRESS ACCESSORIES

Federal Pre ss Co.

Fig. 2·1-A. Typical gop-frame press.

frame is C-shaped to provide accessibility for loading and unlo·ading work. They are used: 1. When strips or sheets are fed from right" to left or from left to right 2. When strips or sheets are fed from front to back 3. When individual blanks are inserted in the die for secondary operations. Gap-frame presses are built in capacities ranging from 1 to 315 tons pressure. They may be: 1. Inclinable 2. Non-inclinable 3. Single-action 4. Double-action 5. Back-geared. The frame of an inclinable gap-frame press may be tilted back to an angle of thirty degrees. This permits finished workpieces to slide to the rear of the press upon completion. Single-action presses are provided with a single ram. They are used for blanking, bendin g, forming and other operations. Double-action presses contain an inner ram sliding within an outer ram. They are used for severe forming and drawing operations. Back-geared presses are provided with gears for slowing the stroke and increasing the power. To enlarge your understanding of the gap-frame press, consider Fig. 2-1-A which shows a representative flywheel press. One revolution of the flywheel causes the ram to make a downward stroke and an upward stroke, thus completing one cycle. Fig. 2-1-!3 shows a back-geared press. Gearing increases the capacity of the press. Each press is composed of the followi ng elements:

Fede ral Pres s Co. Fig. 2·1-B. Typical gap·f rame press with bock-gearing.

A. B. C. D. E. F.

Frame Assembly Ram Assembly Crankshaft Assembly Back Gear Assembly (gea red presses) Trip Assembly Reclining Mechanism (inclinable presses).

2-2. FRAME ASSEMBLY The exploded drawing at A shows the frame assembly of a representative flywheel press. The view at B shows the frame assembly of a geared press. Frame 2 is provided with legs 14 fastened together with tie rods 15. Bolster plate 9 is fastened to the table of the frame after holes have first been machined in it for passage of slugs and blanks . At the upper portion of the frame, seats are machined for the crankshaft, and bearing caps 6 retain it in position. Following is a complete list of parts in the frame assembly. Locate each detail in the illustration to familiarize yourself with the names and shapes of machine parts: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Frame (Back gear type) Frame (Flywheel type) Bronze bushing Bushing screw Felt pad Bearing cap Bearing cap oil cup Bearing cap screw Bolster plate Bols te r plate bolt

11. 12. 13. 14. 15. 16. 17. 18. 19.

Bolster plate washer Bolster plate nut Le g bolt Le g Le g tie rod Tie rod nut Leg Le g bolt nut Leg capscrew.


22

~~

~}~):'\ ' \ .':.,) 6

Federal Press Co.

Fig. 2-2. Exploded views of the frame of a flywheel press (A) and of a geared press (B).

2-3. RAM ASSEMBLY This exploded drawing shows all of the components that are included in the ram assembly. The ram 27 is the working member of the press and it is important that you understand its construction thoroughly because it can affect the design of many parts of the die. The ram is reciprocated up and down by a crank through pitman 6 while confined and guided in Vshaped gibs 17 and 33 . The gibs, in turn, are fastened to the press frame. Ram adjusting screw 11 is provided with a hardened ball end that engages the ball seat 13. Both are confined in the ram by spanner nut 9 tightened with spanner wrench 10. The threads of ram adjusting screw 11 engage a hole tapped in the bottom of pitman 6. The pitman is slotted for clamping the ram adjusting screw with pitman clamp yoke 34 and nuts 7. Ram ad-

justing screw 11, therefore, adjusts the position of the ram, raising it or lowering it as required. To make an adjustment, nuts 7 are loosened and ram adjusting screw 11 is turned with wrench 12 raising or lowering the ram depending on the direction in which the screw is turned. Nuts 7 are then tightened to prevent further rotation of screw 11 when the press is operated. Clamp 26 fastens the shank of the die set for reciprocating the punch half of the die up and down. Two studs 25 are threaded into holes in the ram with a tight fit. Turning nuts 23 then clamps the punch shank . The ram of the press exerts force to pierce, blank, or perform other operations . The magnitude of the force depends upon the rated capacity of the press. Capacities are specified in tons and the most commonly used presses range from one ton to 150 tons.

23


2-4. CRANKSHAFT ASSEMBLY

35

The diameter of crankshaft 25 which is engaged by the pitman of the ram is turned eccentric with the rest of the shaft by one-half the amount of stroke required in the ram. At one end a brake drum 26 is engaged by brake shoes 30 and 35. The braking action stops the shaft quickly when clutch pin 21 is disengaged from the driving flywheel 45. An electric motor is mounted on motor bracket 57 or 58. Sheave 52 is keyed to the the motor shaft and it drives the flywheel through Vbelts 53. Study carefully the manner in which bearings are applied, construction of the brake, and the way in which clutch components go together. As you go through the following list of parts, study each in turn in the illustration until your understanding of the crankshaft assembly is complete:

gr--'

~

~ 5

·~,!t 10

'

- - ·-

1. 2. 3. 4. S. 6. 7. 8. 9. 10. 11. 12.

! t--8

' -----t:: g,

11

.

16

18

I

~

20

·~· J I,

33

22

J~

18

t ig. 2-3. Exploded view of the ram assembly.

Federal Press Co.

Study the following list of names of parts and actually look up each one iri the illustration to familiarize yourself with the construction of the ram assembly:

1. Pitman oil cup . Pitman cap screw 3. Pitman cap -l . Pitman felt pad - . Pitman bronze bushing 6. Pitman . Pitman clamp yoke nut . Set screw 9. Ram ball nut :o. Spanner wrench : 1. Ram adjusting screw : . Adjusting screw wrench : 3. Ra m ball seat :·t Gib set screw jam nut :5. Gib set screw : 6. Gib oil cup : i . Gib, right hand : . Washer

19. 20. 21. 22. 23. 24. 25. 26. 27 . 28. 29. 30. 31. 32. 33. 34. 35.

Gib cap screw Knockout bracket, right hand Washer Knockout bracket screw Ram clamp stud nut Ram clamp stud washer Ram clamp stud Ram clamp Ram Knockout bracket, left hand Knockout bar clip Knockout bar Knockout bar spring Knockout bar spring clip Gib, left hand Pitman clamp yoke Pitman bushing fastener

Brake release cam stud Brake release cam Brake release cam lever Taper pin Cam lever screw Brake release shaft Brake band set screw Jam nut Washer Cam stud nut Cam lever nut Brake band set screw 13. Jam nut 14 . .Trip latch stud taper pin 15. Trip latch stud 16. Frame bushing 17. Brake release shaft 18. Non-repeat cam screw 19. Non-repeat cam 20. Crankshaft ring 21. Clutch pin 22. Clutch pin spring 23. Clutch pin safety stop assembly 24. Clutch pin spring support 25 . Crankshaft 26. Brake drum 27. Brake spring 28. Brake handwheel 29. Jam nut 30. Brake band, lower

31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42 . 43. 44. 45. 46. 47. 48. 49.

SO. 51. 52. 53. 54. 55. 56. 57. 58. 59.

Brake lining Brake lining rivet Hinge pin lock ring Hinge pin Brake band, upper Brake screw; upper Brake band adjusting screw Flywheel hub cap Hub cap screw Crankshaft end plate screw Crankshaft end plate Bearing cone Bearing cup Flywheel bearing spacer Flywheel Flywheel backup pin Flywheel drive pin Alemite fitting Bull gear guard Flywheel guard Tight pulley guard Motor sheave V belt Motor bracket hinge rod Motor bracket adjusting screw Adjusting screw washer Motor bracket (Flywheel type) Motor bracket (Back gear type) Motor bracket set screw.

2-5. BACK GEAR ASSEMBLY In a back geared press, considerable mechanical advantage is realized and the ram exerts more force. This occurs because the flywheel 26 is not mounted directly on the crankshaft for driving the ram. Instead it is positioned to the rear of the crankshaft and keyed to back gear shaft 23 by means of key 24. At the other end of this shaft is keyed pinion 4 which drives the bull gear 5 mounted directly on the crankshaft. A back geared press operates at a slower speed. Pinion 4 makes a number of revolutions for each revolution of gear 5. Following is a list of the parts in the back gear assembly:

24

Federal Press Co.

Fig. 2·4. Exploded view of the crankshaft assembly.

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Bull gear backup pin Bull gear drive pin Back gear pinion key Back gear pinion Bull gear Bearing cone Bearing cup Bearing spacer Crankshaft end plate Crankshaft end plate screw Bull gear hub cap Hub cap screw Unit housing Bearing cup

15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Bearing cone Spacer ring Adapter Large piston ring Small piston ring Adjustment nut Adapter nut Lock washer Back gear shaft Tight pulley key Alemite fitting Tight pulley Back gear shaft end plate End plate screw Adapter nut spanner wrench.

2-6. TRIP ASSEMBLY The trip assembly is a linkage system for engaging and disengaging the clutch pin for operating the press. Essentially it consists of the trip pedal 33 which operates the latch 25 - 26 through trip rod 22. When the operator 'depresses the trip pedal with his foot, the press will operate continuously as long as the pedal is kept down. For a single stroke of the ram, the pedal is depressed and quickly released. The clutch pin will then engage the flywheel to turn the crank a single

revolution after which it becomes disengaged to s tot: the press. Study the following list of names of parts the trip assembly and compare with the views in e illustration: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Latch stud Latch bracket Latch bracket screw, upper Latch bracket screw, lower Fulcrum lock screw Latch trip bar fulcrum lock Fulcrum lock spring Latch release lever spring Release lever spring guide Spring guide ball roller Roller nut Roller washer Non-repeat release lever roller assembly Non-repeat release lever Latch roller Latch roller stud Trip rod swivel set screw Latch trip bar stud Latch trip bar Trip rod swivel spacer Trip rod swivel Trip rod

23. 24. 25. 26. 27. 28. 29. 30. 31. 32 . 33. 34. 35. 36. 37. 38. 39. 40. 41. 42.

Latch spring Latch spring guide Latch (Flywheel type ) Latch (Back gear type ) Latch roller stud was her Latch roller stud nut Latch spring guide bushing lock Latch spring guide bus Fulcrum set screw Latch trip bar fulcru m Trip pedal Trip rod clip Trip pedal screw Trip pedal spring guide clip Trip pedal spring guide Trip pedal spring Spring guide washer Spring gui de jam nut Trip pedal guide se t screw Trip pedal guide.

~

25


Federal Press Co.

Fig. 2·5. Exploded view of the back gear assem bly.

2-7. RECLINING MECHANISM The reclining mechanism is operated to tilt the frame to an angular position. This is necessary for some operations when an upper knockout is incorporated in the die . The ejected part then slides to the rear of the press by gravity. One type of reclining mechanism consists of the cast bracket 1 engaged by reclining screw 2 which is threaded into the gear 3. Reclining lever 4 engages one of the notches in pinion 7 to tum it, and this rotates gear 3 moving the reclining screw 2 laterally. The frame is either raised or lowered depending on the direction in which pinion 7 is turned by lever

25 26

3~

.L--·

4.

J-22

In another type of reclining mechanism shown at the lower right, a worm 11 turned by worm shaft 9 inclines the frame. Larger presses may be reclined by a hydraulic mechanism. Following are the names of parts that comprise the reclining mechanism:

j

Fede ral Pres s Co. ~

;. 2-6 . Exploded view of the trip assembly.

1. Rec lining bracket 2. Reclining s crew 3. Reclining gea r nut

4. Reclining lever 5. Re c lining lever bracket 6. Reclining pinion shaft

26


Fede ral Press Co.

Fig. 2-7. Exploded view of the reclining mechanism.

7. 8. 9. 10.

Reclining pinio n Re clining wor m shaft clip Reclining worm shaft Worm shaft bushing

11. Reclining worm 12. Reclining bracket 13. Bracket scre w.

2-8. LARGE GAP FRAME PRESSES Gap-fra me presses are built by a number of manufacturers and the outside appearance of each make differs somewhat from that of other makes. The illustration shows an inclinable 75 ton Niagara gap-frame press. This is an automated machine; that is, it is provided with outlets for operating auxiliary devices. Circulatin g lubrication has been built into the legs and through the entire machine and a special limit switch operates the connections for automation devices.

2-9. OPERATING A GAP-FRAME PRESS This shows a gap-frame press in operation at the Warner Electric Clutch and Brake Company plant. This is a secondary operation job of forming round rings. The operator places a blank into the die with lon g aluminum tongs. Tripping the press causes the ram to descend and the blank is formed between the punch and die block. The completed part is removed with the tongs and another blank is placed into position . This process is repeated until the number of parts required have been formed . After a run has been completed, the die is removed from the press and another die is mounted in position for producing other parts. Operations performed in this press include piercing, blanking, forming, assemblin g, and many others.

2-10. DIAL PRESSES

Niagara Machine & Tool Wo rks Fig. 2-8. Typical la rg e gap-frame press .

A special type of gap-frame press is called a dia press because it is provided with a dial or turret for increased safety in loading and unloading workpieces . Dial presses are used for secondary operations such as

PRE SES AND PRESS ACCESSORIES

27

Federal Press Co.

Fig. 2·10. Typica l dial press.

Clearing Division of U.S. Industries, In c.

- -

·9. Forming round rings in a gap-frame press.

: =cing,

marking, bending, forming, and assembly. are loaded in nests at the front of the press and ·- ~; a re carried by the dial into position under the ram - e the work is actually performed. Thus, the opera·: s ha nds need not be introduced under the ram. A - :: press may be provided with an ejector or a pickoff -- anism for removing the parts from the dial automat. ·} . In addition, it may be provided with a probe _ =·' on. The probe enters one of the dial stations to ·-·e ine if blanks have been positioned properly be-- - hey move into place under the ram. -~.s

. DIAL ASSEMBLY is exploded drawing shows all of the components ::: a re included in the assembly of a representative ::~ feed . The dial work plate 1 .is fastened to index ~ =·e 9. Under the index plate are fastened twelve _:...ers 10, free to turn on studs 11 and 12. Cam 20, ed to shaft 19, is turned by the crankshaft of the

press through bevel gears 38 and 48 and shaft 19. One revolution of cam 20 causes the dial work plate 1 to be indexed one station. Indexing occurs rapidly as the angular shoulder of cam 20 acts against one of the rollers 10. Durin g the remainder of the revolution of cam 20, the dial work plate 1 is stationary and the work operation is performed by the dies in this period of dwell. Holes are jig bored accura tely in dial work plate 1, and hardened bushings 8 are press-fitted into them. A long ground pin, fastened in an arm extending from the press ram, engages each hole in turn for final precise positioning of the dial plate before work is done. Should the dial plate not be fully indexed as would occur if a key were sheared for any reason, the pin would retract and actuate a trip to stop the press before damage occurred to either the press or the dies. Compare the names in the following list with the parts shown in the illustration to increase your knowledge of the construction of a dial press: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Dial work plate Work plate washer Work pla te screw Center stud screw Center stud was her Center stud plate Dial work plate oiler Safet y s top wear bushing Index plate

10. 11. 12. 13. 14. 15. 16. 17. 18.

Index plate r oller Index rolle r drive st ud Index rolle r s tud Dial base dowel Dial base Dial cente r stud Dial base cap scr ew Dial base washer Index cam key


28

Federal Press Co.

Fig. 2·11. Exploded view of o diol feed ossembly.

19. 20. 21. 22 . 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33 . 34. 35. 36. 37 . 38. 39.

Cam shaft Inde x cam Cam shaft bushing, right Cam shaft bushing key Cam shaft adjusting nut Cam shaft set screw Cam shaft bearing cap Bearing cap screw Cam housing cover oiler Cam housing cover Housing cover screw Cam shaft bushing, left Thrust collar set screw Cam shaft thrust collar Cam s haft thrust bearings Cam shaft hous ing s et screw Cam shaft housing alemite fi tting Cam s ha ft hous ing Cam shaft beve l gear pin Cam shaft bevel gea r Shear pin drive collar set screw

40. 41. 42. 43 . 44. 45 . 46. 47 . 48. 49 . SO. 51. 52. 53. 54 . 55. 56. 57. 58. 59. 60. 61.

Shear pin drive collar Shear pin Lower gear housing cover Lower gear housing Lower gea r housin g screw Housing support bracket Bracket cap screw Bracket cap screw washer Vertical shaft bevel gear Bevel gear pin Vertica l drive shaft Vertical drive shaft housing Vertical shaft thrust bearing Upper gear housing screw Upper gear housing Crankshaft thrust bea rin g Thrust collar set screw Crankshaft thrust collar Thrust collar alemite fittin g Gear housing oiler Crankshaft beve l gear Bevel gear pin

29


2-12. SAFETY STOP AND TRIP ASSEMBLY The safety stop at A consists of plunger 29, plunger adj ustment 28, and jam nut 27. The assembly is held · n bracket 24 which is mounted to the ram of the press. P unger 29 enters hardened bushings 8 of Fig. 2-11, as previously explained. Should the plunger strike the dial table surface instead, it retracts actuating trip bar 26 to stop the press. The trip assembly B of the dial press is not foot. era ted. Instead, a hand lever 17 is used to actuate ~e trip latch 10 for engaging the clutch. Study names the following list and match the names with the arts in the illustration to understand the construction the safety stop and of the trip assembly:

! . Latch spring adjusting nut clamp • . Latch spring adjusting nut 3. Latch bracket . Latch bracket screw ,;. Latch spring • . Latch spring guide - . Latch stud nut, large . La tch stud washer . La tch stud _~. Trip latch .1 . Washer :_. La tch stud nut, small . 3. Trip lever connection clip _ .. Trip lever connection

15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Trip hand lever spacer Trip hand lever stud Trip hand lever Safety stop mounting block Mounting block screw Safety stop block spring Safety stop spring plunger Safety stop trip lever Safety stop bracket clamp Safety stop bracket Safety stop bracket screw Safety stop trip bar Plunger adjustment jam nut Plunge r upper adjustment Safety stop plunger. Federal Press Co.

Fig. 2·13. Conveyor feed press.

2-13. CONVEYOR FEED PRESS This illustration shows a gap-frame press equipped with a conveyor feed for bringing workpieces into position under the die. The conveyor feed performs the same function as the dial of a dial press. That is, it makes the press safer for secondary-operation work because the operator's hands need not be placed under the ram.

2-14. HORNING PRESSES A horn press is a special gap-frame press provided with a large horizontal hole in the frame into which horns of various sizes and shapes may be inserted for seaming metal drums, piercing, forming, and many other operations. Vertical horns may be inserted in the hole in the base for punching holes in the bottoms of shells, curling, wiring, and other operations .

S \21 28

29

~23 24

A

.r.--

~!,,J

0

8 21

Federal Press Co. ·

- ; . · 12. Exploded views of safety stop (A) and trip assembly (B) : : ial press.

2-15. END-WHEEL PRESSES End-wheel presses ar~ gap-frame presses provided with a right-angle drive. In this type of press the flywheel and gearing are positioned at the rear and the crankshaft extends from front to back instead of from side to side. Small end-wheel presses may be used to drive sub-press dies for producing watch, clock, and


30

Fig. 2·15. End-wheel press.

Thomas Machine Mfg. Co.

Fig. 2-14 Horn or horning press.

instrument parts. Larger ones blank, curl, and perform other conventional press operations. Sizes range from small bench types to large presses with capacities of one hundred tons or more.

2-16. HYDRAULIC PRESSES Hydraulic presses have characteristics which make their action different from that of mechanical presses. In operation, the ram has a rapid travel to the workpiece, a controlled dwell, and a rapid return. They may be set so that, upon contact with the work, a predetermined force is built up. When this force is reached the ram retracts. This feature makes them particularly useful for assembly operations where workpiece thicknesses may vary. The following characteristics of hydraulic presses make them particularly adapted for some work: 1. The maximum force obtainable is available throughout the entire length of the stroke . 2. The force exerted during the working portion of the stroke can be accurately predetermined and regulated. 3. The rate of travel can be adjusted for the requirements of the work.

Ferracu.te Machine Co.

4. As previously explained, the working stroke adjusts itself automatically to work requirement. Hydraulic presses are particularly adapted for assembling, marking, broaching, cold forming, straightening, and similar operations. Large hydraulic presses are in constant use for many forming and drawing operations.

2-17. CONSTRUCTION This cut-away view shows the construction of a representative gap-frame hydraulic press. Observe that the base is the reservoir for hydraulic fluid. A motor at the upper right drives a pump directly below it for transferring fluid to either the top or bottom of the piston at the upper left. The piston is the ram of th e press. When fluid is pumped above the piston, the ram goes down. When fluid is pumped below the piston the ram is raised. Hydraulic valves control direction and pressure.

2-18. HYDRAULIC DIAL PRESSES Small and medium-size hydraulic presses may be provided with a hydraulically operated dial table. This six-station index table is interlocked through the hy-

31

" ES AND PRESS ACCESSORIES

Denis on Engineering Div., American Brake Shoe Co.

Fig. 2·17. Cut· away view of a hydraulic press.

=

Denison Engineering Div., American Brake Shoe Co.

draulic system of the press for positive sequence of movement. The table dial may be regulated through a stepless range of from 10 to 70 indexes per minute by adjusting a knurled knob on the fluid motor drive. Two types of automatic ejection of parts can be provided "cam liftout" and "punch through". With the former

· 16. Hydraulic press.

Denison Engineering Div., American Brake Shoe Co.

= ;. 2·18. Hydraulic dial

press.

A. Schrader's Son

Fig. 2·19. Pneumat ic press.


32

a cam may be positioned within the table housing to eject the parts out of ~heir nests . To provide punchthrough removal of blanks, a section of the table housing is removed.

2-19. PNEUMATIC PRESSES Presses operated by compressed air are used for pressing, riveting, staking, cut-off, marking, crimping, and other operations on small parts and assemblies. They are available as single-acting for impact jobs; double-acting for squeeze and power withdrawal. Control and speed of the cylinder and ram can be varied by using standard air control accessories.

2-21. STRAIGHT-SIDED PRESSES A straight-sided press is composed of a base, two vertical sides, and an upper member called the crown. This construction provides capacity for withstanding heavy operating loads without deflection. Straight-sided presses are used for all press operations such as blanking, trimming, bending, formin g, drawing, and others, in large dies and for heavy gages of stock. Feed of material strip is from front to back. Like gap-frame

2-20. ELECTRIC PRESSES The electric press is also used for pressing, riveting, staking, marking, and other similar operations on small parts and assemblies. The Electropunch is an electro-magnetic impact hammer consisting of a solenoid and a plunger, both mounted on a single adjustable bracket. When the switch is closed, electricity energizes the solenoid and the plunger delivers a!\ impact to the ram which holds the tool. When the switch is

Niagara Machine & T ool Works

Fig . 2·21. Typical straight·sided press.

presses, straight-sided presses may be of the flywheel type or the geared type. They are built with single, double, or triple action rams. Until comparatively recently, most progressive dies were designed for use in gap-frame presses. However, the current trend is toward progressive dies in straight-sided presses instead because of the increased rigidity provided by them.

2-22. STRAIGHT-SIDED DIAL PRESS

Black & Webster, Inc.

Fig. 2·20. Electr ic press.

Like gap-frame presses, straight-sided presses may be provided with a dial feed. Workpieces are loaded at the front of the press and they are carried by the dial to working position under the ram.

2-23. HYDRAULIC STRAIGHT-SIDED PRESSES opened a spring rapidly returns the plunger, ready for the next operation. An attachment called an Automatic Repeating Control causes the electropunch to deliver repeated blows at the rate of three per second as long as the haRd or foot switch is closed. This continuous action is well-adapted for riveting, swaging, peening, and the like, where a number of rapid, repetitive strokes are advantageous.

Straight-sided presses may be operated hydrauli.cally. This 1000 ton press can be adjusted for rapid traverse and correct drawing speed. Each hydraulic action is provided with an independent control. Unlike mechanical presses that develop maximum thrust near the bottom of the stroke, hydraulic presses are capable of applying their maximum force throughout the length of the stroke.

PRE

33

ES AND PRESS ACCESSORIES

ing the largest stampin gs now being produced. This is a mechanical four-post press equipped with a roll feed for running stri ps through the dies automatically . Strips may be run through four-post presses either from side to side or from front to back . Many four-post presses operate hydraulically .

2·26. ALL-STEEL FOUR-POST PRESSES The posts of a fou r-post press are not necessarily round . This 200 ton press has a welded steel frame construction . Rolled steel plates are cut to shape, in terlocked, and welded into rigid box sections. Within the square posts are heavy steel tie rods for increased rigidity.

Federal -Wcuco Div., The McKay Mac hine Co.

=2· 2·22. Straight-sided dia l press.

-24. LARGE STRAIGHT-SIDED PRESSES S raight-sided presses can be very large machines . • is is the Danly Q.D.C. (Quick Die Change) press in · ·ch the die can be located and attached to a bolster :;:..a•e outside the press while a first die is being oper::.:ed in the press. In effect, the press is turning out _·ampings and the tools are being set up for the next :· uction run simultaneously . To accomplish this, ""ch press is equipped with two bolsters mounted on :arriers. Each bolster plate and carrier make up a die :A: ier assembly. The die carriers move into or out of the working ·,rea · :ier the ram on tracks perpendicular to production ::- w. The die carriers are individually motor driven they are moved into working position against itive stops before clamping occurs.

:-25. FOUR-POST PRESSES Four-post presses are composed of a base on which : -e mounted the posts or columns that support the ::: wn. Posts provide accessibility as well as a large rking area. Four-post presses range from medium:!Ze, high-speed machines like the 25 ton press illus. "' ed here to very large presses for forming and draw-

HPM- Division Koehring Co.

Fig . 2.23. Hydraulically ope ra ted sH aight·sided press •

34

PRESSES A D PRESS ACCESSORIES

Danly Machine Specialties, Inc .

Fig. 2·24. large straight-sided press.

2-27. LARGE FOUR-POST PRESSES This is a giant 7000 ton rubber pad forming press. Such presses are used for forming and drawing large aircraft and missile components and for producing other large stampings.

2-28. TRANSFER PRESSES

Havir Manufact uring Co .

Fig. 2-25. Typical/our-post press.

..

'

~

We come now to another interesting type of press, the transfer press. Such presses are provided with a number of stations and a transfer mechanism for moving workpieces from station to station. At the first station a blank is cut from the strip. It is then moved through the other stations where other operations such as . drawing, piercing, embossing, slitting, trimming, etc. are performed on it. A completed part is d.e livered at the final station. Properly tooled , transfer presses are rapid and efficient producers of stampings. A recent trend has been the development of larger and larger transfer presses. The Clearing Trans flex press is produced in capacities from 75 through 300 tons. It is possible to have as many as sixteen die stations in a single press .

35


Lake Erie Machinery Corp.

Fig . 2· 27. Larg e four-post press.

Ve rson Allsteel P ress Co.

"•9·

2·26. Four-post press with wel ded steel frame construct ion.

-29. HYDROFORM PRESSES The hydroform press forms and draws stampings flat blanks by an interesting hydraulic process. : ooling is simple and consists of a punch and draw ..: g only . The upper die is an oil-filled chamber cov:::ed by a flexible diaphragm . Hydroform presses are ailable to form blanks ranging from 8 inches to 40 _ cbes in diameter. In hydroforming, the blank is placed over a punch ::: d draw rin g. The upper forming chambe r is lowered - . er th e blank. Hydraulic pressure is then applied ...... sing the draw ring to go down as the blank is formed _. er the lower punch. After the part has been fully :_-awn the pressure is released, the forming chamber - raised, and the finished part is stripped from the _ ch by the draw ring. :':0::1

The Baird Machine Co.

Fig. 2·28. Ty pical transfer press.

6436


36

2-31. FOUR-POST UNDERDRIVE PRESSES This underdrive press is provided with four posts for driving the punch holder of the die. A 60 ton machine, it is provided with auxiliary devices that include feed rolls, scrap chopper, and centralized lubrication system.

Meta-D y namic s Div ., Cincinnati Milling and Grinding Machines, Inc .

Fig. 2-29. Hydrofo rm pre ss.

He nry & Wright, HPM- Division Koehring Co.

2-30. UNDERDRIVE PRESSES The next press classification that we shall consider is called the underdrive press, so called because the driving mechanism is located under the bolster plate instead of above the ram as in conventional presses. The upper press member is simply a platen reciprocated by posts that pull it down and then raise it. The press illustrated here is provided with two posts for driving.

Fig . 2·31. Four-post underdr ive press.

Larger underdrive presses are available. Some are in the 200 to 300 ton range and are used for heavy duty mass production. One 300 ton press, provided with eight driving posts, was designed for progressive dies up to 12;6 feet in length .

2-32. SUPER HIGH-SPEED PRESSES We will close this discussion of presses by considering presses that attain incredibly high speeds because the strip is not stopped while work is bein g performed on it by the die. Instead the strip is run continuously and the punch and die are reciprocated to cut blanks while the strip is in motion. One of these high-speed presses is the Wean "Flying Press" designed to run at 600 strokes per minute with a nine inch length of feed. Stock is moved throu gh the press at a rate of 5400 inches per minute.

2-33. BLISS SUPER HIGH SPEED PRESS Diamond Machine Too l Co rp .

Fig. 2-30. Underdrive press.

This is the Bliss Strip Feed Press, another of the super high -speed presses. Motions are controlled fro m the control panel at the right of the machine.


37

of the cy tinder is ordinarily in con tart with the underside of the bolster plate and therefore flush with the surface of the table of the frame. Die knockouts are provided with pins that extend down to the surface of the cylinder. When the die closes, the pins push the cylinder down against the air pressure by the amount of knockout travel. When the ram goes up, the cylinder pushes the pins upward to operate the knockout. The die cushion can be set for exactly the amount of force required and the maximum force obtainable is available throughout the entire len gth of the stroke.

The Wean Engineering Co., Inc .

=ig. 2-32. Wea n super high-speed press.

Dayton R ogers Mfg. Co .

Fig. 2·34. Pneumatic die cushion mounted in position under press.

2-35. HITCH FEED

E. W. Bliss Co .

= g. 2-33. Bl iss super high-speed pres s.

The next accessory that we shall consider is the hi tch feed, a device for feeding s trips through a die automatically. A hitch fee d is fastened directly to the die set and it becomes a part of the die assembly. In operation, a side cam fastened to the upper punch holder contacts a roller mounted on the slide of the hitch feed and it caus es it to move to the right. This moves the sliding hitch to the right also. The hitch is a bent metal tab held loosely by a small cap screw and backed up by a small coil spring. Underneath it is a hardened plate on which the strip rests. When the ram goes up, a heavy spring moves both slides to the left. In this direction the hitch tends to pinch the strip because of

P'R ESS ACCESSORIES The first press accessory to be considered is the ::- eumatic die cushion used to apply controlled thrust : om under the press. It is important that the die de~ · gner understand its construction and operation becaus e many dies are provided with knockouts that are rated by it. The cushion is composed of a large -:linder, a plunger, and four tie rods. Air hoses connect :· with the compressed air system of the plant.

-34. OPERATION OF THE DIE CUSHION This shows the pneumatic die cushion mounted in ::: ition under the press. The frame is threaded for =---gagement of the tie rods. Observe that the surface

H. E. Dickerman Mfg. Co.

Fi g. 2·35. Hitc h Fee d.

38


its angle and the strip is moved to the left until it contacts a stop. When the. slides are moved to the right by the cam, a stationary hitch at the far right pinches the strip to prevent it from backing up.

2-36. DIE FEED The die feed is also mounted to the die set and it operates in a s imila r manner. Instead of the "hitch" principle, the strip · is engaged by two opposed rollers mounted on the movable slide and by another set of opposed rollers mounted on the stationary frame of the feed. Built within the rollers is a mechanism which permits them to turn in one direction only. When it is

F. ]. Littell Mac hine Co. Fig. 2·37. Roll feed operated by driving di sk fa stened to crankshaft.

H. E. Dickerman Mfg. Co.

Fig. 2·36. Die Feed.

attempted to turn them in the other direction, they lock. In operation, the double cam on the punch holder contacts the slide causing it to move toward the right, the rollers on the slide turning freely. The rollers on the frame lock, preventing the strip from backing up. When the cam goes up, the rollers on the slide lock and they move the strip towards the left, the rollers on the frame now turning freely.

F. } . Littell Machine Co. Fig. 2·38-A. View of rol l feed showi ng disengagement by overrunnin g clutch.

2-37. ROLL FEEDS Another method of feeding strips through- a die automatically is by means of a roll feed mounted on the bolster plate of the press and operated by a driving disk fastened to the crankshaft. The spring-loaded rolls advance the strip a preset amount, usually to 0.010 inch past register. Near the bottom of the stroke, an arm mounted on the ram contacts the roll feed to disengage the rolls. Pilots incorporated in the die enter previous ly pierced holes in the strip to effect perfect register.

F. ]. Littell Machine Co. Fig. 2·38-B. View of ro ll feed showing engagement by overrunning clutch.


39

2-38. OPERATION OF A ROLL FEED This shows the operation of a representative roll feed; this one operated by gears instead of by a crank. Rack B is operated by the driving disk on the crank· shaft. As it moves downward it turns pinion X which turns drum D through a sleeve. In other words, drum D, pinion X and the connecting s leeve are all in one piece. The sleeve and pinion have an axial hole which engages shaft C. An overrunning clutch Z is keyed to the shaft. During the downward travel of the rack, shaft C does not turn because rollers Y are disengaged. When the rack goes up, drum D drives shaft C because the rollers become wedged between drum D and blocks Z.

2-39. ROLL FEED DRIVE This shows the complete drive for a single roll feed and for a double roll feed, with a strip shown being advanced by the r~lls in both views . To the end of shaft C in the previous illustration is fastened a helical gear and this drives another helical gear at one end of the lower roil. At the other end of the roll is a spur gear which drives another spur gear on the upper roll.

2-40. DOUBLE ROLL FEED Roll feeds are usually mounted on either or both sides of a press and also sometimes at the front of a press. This shows two roll feeds mounted on a large Minster press . One is mounted at the right and one at the left side of the press. Double roll feeds are used for feeding heavy stock beyond the capacity of a single feed.

..

(

2-41. FEEDING AND STRAIGHTENING This is a heavy-duty feeding and straightening machine capable of s traightening and feeding coil stock up to 0.125 inch thick. It will feed up to 19 inch lengths at s tandard speed of 40 strokes per minute.

F. ]. Litt ell Machine Co.

Fig. 2·40. Two ro ll feed s mounted on o press.

2-42. STOCK REELS When strip is fed to a die from a large coil, the coil is mounted in a stock reel for delivery to the press . This illustration shows a motorized stock reel in which a coil has been clamped. The motor is started and stopped by a switch -arm control shown at the front above the stri p. The stri p fo rms a loop which is raised as mate rial is used by the die. When the switch-arm control has been raised in a preset amount, it starts the motor through a mercl!ry switch . The turning reel

F. ] . L ittell Machine Co.

F. ]. Litte ll Machine Co.

Fig. 2-39·A. Drive lor single ro ll fe ed.

Fig. 2·39-B. Drive for double roll feed.

40


F. ]. Littell Machine Co .

Fig. 2·42. Typical motorized stock reel with coi l. F.]. Littell Machine Co.

Fig. 2-41. Heavy-duty feed ing and straightening machine.

delivers material faster than the die can use it and as the loop increases sufficiently, the switch-arm control shuts off the motor. Thus , the roll feed draws material from the loop instead of having to pull against the heavy coil with possible slippage.

2-43. COMPLET E AUTOMATED PR ESS To automate this press completely , a motorized stock reel and a feeding and straightening machine have been installed. After the end of a new coil has been started through the press, all operations a re automatic until the end of the coil has been reached .

TRANSF ER ATTACHMENT S Automatic press lines for handling coiled strip have long been standa rd whenever high production rs required. A more recent development, at least for large parts, has been the automatic transfer of stampings from one station to another. An example of a transfer press was shown in Fig. 2-28 . In addition, a number of auxiliary attachments have been developed for converting conventional straight-sided and four-post presses into transfer presses. One such transfer device is the Sheffield Press Pacer. The unit consists of a pair of rails, one mounted on each side of the die, on which are mounted pairs of opposed pickup fingers for transferring the parts from station to station. When used in a press, the transfer motion is entirely mechanical, being obtained by means of a lever ann

mounted to the press ram. The press so equipped may be fed from right to left or front to back, loaded and unloaded either automatically or manually. Press Paoers are also used to transfer parts from one press to another. An electric motor drive produces the indexing movement.

AUTOMAT IC UNLOADERS Another phase of press automation - of making operations automatic - concerns the unloading of presses after operations have been performed. One type called an "in line" unloader is applied at the rear of the press, and it is sequenced so that its arm moves forward on the upstroke of the press. Special gripping fingers engage the workpiece and withdraw it from the die . Near the end of the return stroke the fingers open and the part is dropped into a box. This unloader is used in small and medium presses.

2-44. IRON HAND UNLOAD ER The "Iron Hand" is a versatile unloader for large presses. Upon completion of the operation the arm swings into the die area and gripping fingers clamp on the edge of the stamping. The arm then swings out removing the part from the die. It is then usually deposited on a conveyor for transfer to the next ope ration. In the illustration, eight pound oven liners fo r Hotpoin electric ranges are removed from a 250-ton Clearin g press .


41

F. ] . LittellMachine Co.

Fig. 2·43. Automated press setup wi th mo torized stock reel , feeding and str aigh tening machine, and pres s.

Sahlin E ngineering Co ., Inc .

Fig . 2·44. " Iron Hand" unlaaders removing parts from presses.

Section 3

THE MATERIAL STRIP 3-2. SLITTING

Now that you have acquired an understanding of the press and of its accessories, you will have to learn about the material strip - about the ribbon of metal or other material that is run through the press in order to produce stampings. Six elements of information will be included: 1. How strips are produced 2. How strips are planned 3. Materials from which strips are made 4. Deformation of sheet materials 5. Theory of cutting sheet materials 6. Types of strip edges.

Slitting machines for cutting strips are a relatively new development. In slitting, the sheet is fed through rotating cutting rolls and all strips are cut simultaneously. In the illustration, cutting rolls A are mounted the proper distances apart 9n arbors B. The cutting edges of the rolls are separated by the required amount of clearance to effect cutting of the material as shown in inset C. Turning the rolls under power causes the sheet to advance and it is cut into strips. As many as twenty or more strands can be cut at one time. In other types of slitters, the sheets are pulled through the rolls instead, and the rolls are free to turn. Slit strips are very accurate both in width, flatness, and in parallelism of sides because accuracy is built into the machine instead of depending upon the operator. Unlike the shear which can cut strips only as long as the blade, the slitter will cut continuously to any length, without limit.

3-1. SHEARING The oldest and simplest method of producing metal strips is by shearing. In the steel mill, metal is formed into large sheets by rolling and trimming. To cut a sheet into strips, it is introduced under the blade of a shear. Gages register the edges of the sheet for cutting correct widths of strips. Descent of the shear blade causes each strip to be parted from the sheet. Advancing the sheet against the gages brings it into position for cutting the next strip and this process is repeated until the sheet has been cut entirely into strips. The illustration at A shows a sheet in position under the shear blade C ready to be cut. At B, the blade has descended and the strip has been cut from the sheet. The powe r shear can cut material in any direction lengthwis e of the sheet, across the sheet, or at any angle .

A

8

Fig. 3·2. Cutt in g rolls for slitting strip s from sheet.

3-3. PART DRAWING The first step in the actual production of stampings is to order standard-size sheets of the proper size and thickness from the mill. These are then sheared into strips in the shear department. The widths of the strips into which the sheets are to be cut is specified by the die design department. Therefore, let us go over the steps taken in determining strip width so your understanding will be complete. The illustration shows a part drawing of a representative stamping to be produced in a pierce-and-blank die.

A Fig. 3·1. Producing metal strips from sheet by shearing.

42

43

TilE MATERIAL STRIP

95

12i6 I

P I ERCE ~

2 HLS

\

FEED

I~

'E=:i G

l

I~

Fig. 3·3. Typical part drawing.

3-4. BLANK LAYOUTS This shows the two possible ways of running the strip through the die. The blanks may be positioned the wide way necessitating a wide strip, or they may be run the narrow way permitting the use of a narrower strip. These are called blank layouts and it is imporant that you understand exactly what is meant by the erm. A blank layout shows the way in which it is proposed to produce the blank. For both the wide-run and narrow-run layouts, two holes are to be pierced at the first station and the part is to be blanked out at th e second station. It is customary to show small piercing punches solid black. Section lines are applied through larger piercing punches and through blanking !JUnches, as shown. The strip width and the feed are gi ven directly on the blank layout.

Fig, 3-4. Blank layouts necessitating either wide or narrow strips.

~--------------120--------------~

r (I)

v

LL.--_ _. . . . . . . Fig. 3·5. One of the mill sizes available lor cold rolled sheet steel.

3-5. SIZES OF SHEETS Sizes of sheets as they are manufactured by the mill are given in steel catalogs . Here is a representative · st for 1118 Gage (0. 0478) cold rolled steel: 30 by 96 30 by 120 36 by 96 36 by 120 48 by 96 48 by 120 Sheet sizes are always given in inches.

3-6. STRIPS PER SHEET -WIDE RUN The next step is to select the sheet which will be ::lOst economical, that is, the sheet from which a maxi:::Jum number of strips can be cut, leaving a minimum am ount of waste. Strip width is taken from the blank .ayout. Divide the value given into the values for width of sheet" in the steel catalog, and compare :o determine which sheet leaves the smallest remain· er. The illustration shows the sheet divided into tri ps when the representative blank is run the wide ';\ay.

Fig. 3-6. Number of strips obtainable with wide strip blank layout.

3-7. STRIPS PER SHEET -NARROW RUN This layout shows the. same sheet divided into strips when the blanks are to be run the narrow way. More strips are produced from the same size of sheet.

3-8. STRIP LAYOUTS After it has been decided how the blanks are to be run (wide or narrow way), a stock layout is prepared complete with the following dimensions: 1. Strip width. This dimension is used in selecting the proper width of sheet from which strips are to be cut.

THE MATERIAL STRIP

44 2. Feed. This is the amount of travel of the strip between stations. This dimension is used in selecting the proper length of sheet. Two views are applied, ordinarily, and these are e xactly the views of the strip that will be drawn on the die drawing except that an end view of the strip is added to the die drawing. The die is then actually designed around these views. Illustrated at A is a strip layout for a blanking die in which the blank is run the wide way, and at B is sh own a layout in which the blank is run the narrow way. For this particular job, more blanks per sheet are produced when the blanks are positioned the wide way and there is less waste; so all else being equal, this method of positioning the blanks would be selected.

3-9. STRIPS At A is shown one of the strips ready to be fed through the die with blanks to be removed from it positioned the wide way. At B, the blanks are positioned the narrow way in the strip. Five of the parts have been blanked out of each strip. After the strip is run completely through the die, only a narrow scrap bridge is left.

3-10. BLANKS FOR CUT -OFF Dl ES Now let us go through the first steps taken in the production of blanks in cut-off dies. Two of the sides of such blanks are originally sides of the material strip and no scrap bridge is produced as in blanking dies. The illustration shows a representative stampin g having the parallel sides typical of blanks suitable for production in cut-off dies.

100000 A

!Ooooo N

8 Fig. 3-9. Strip s ready for fee ding either th e wide (A} or narr ow (B) way.

Fig. 3·7. Number of strip s obta inabl e with narrow strip blank layout.

F'EED

l _

;;< 16 GA . (.0 598 )

C .R.S .-

-

it

3 15 F E: D 16

-

A

S T RIPS PER S H EE T ' !1, BLAN K S PER STRIP ' 58 B L ANKS PE R SHEET. 696 ~' W. oQ L.o .375

Fig. 3· 10. Typical part for prod uction in cut-off die.

~

I

)

0

0

8

)

STR IPS PER SHEET BLA KS PER STRIP

gj1 30

BL ANKS PER SHEET. 660 WASTE

W.' 1.250 L .' 1.8 75

Fig. 3-8. Compl ete strip layout s for blanks run either the wide (A) or narrow (B) way.

3-11. BLANK LAYOUTS This shows two blank layouts for producing the stamping in the previous illustration. At A, the part is positioned the wide way in the strip. The edges .of the strip are notched at the first station and a rectangular hole is punched. The blank is cut off from the strip at the second station. At B, the part is positioned the narrow way in the strip. Observe how notching punches are sectioned. The heels C which prevent deflection of the punches are shown but not sectioned. At D, short 45 degree lines and a long vertical line represent the "cut off" line.

45

TIIE MATERIAL STRIP

Blank layouts are drawn to explain the proposed operation of a die to others. When a die designer is given a part print of a stamping for which a die is to be designed, he proceeds to lay out a suitable scrap strip. Then he sections significant punches and adds cut-off lines to make the proposal layout clearer. This is the blank layout and it must be approved by the group leader or chief engineer before design of the die is begun. When an outside engineering office is doing the work for a manufacturing company, the blank layout is submitted to the customer for approval.

~-------------- 120 --------------~

r ID

«t

I 1_~--------------------~ Fig. 3-12. Frequently used size of sheet steel.

® Fig. 3·13. Strips per sheet with wide strip blank layout.

A

8 Fig. 3·11. Blank layout for part shown in Fig. 3-10 run, either the wide (A) or narrow (B) way.

Fig. 3·14. Strips per sheet w1th narrow strip blank layout.

3-12. SHEET SIZES

3-15. STRIP LAYOUTS

Next, a steel catalog is consulted to determine what sizes of sheets are available in the required gage and material. The illustrated sheet, 48 by 120 inches, is a frequently used size.

Next a strip layout is prepared and copies are sent to the purchasing department and to the shear department. From the layout, sheets are ordered and, upon delivery, they are sheared to the strip width given on the layout. At A is shown a representative strip layout for a blank for a cut off die positioned the wide way, and at B is shown a layout for a blank positioned the narrow way. For this job we find that exactly the same number of blanks are produced with blanks positioned the narrow way as for "wide-run positioning" and there is no waste in either method. When blanks can be run either way, select the "wide run" method for three reasons: 1. Fewer cuts will be necessary for producing the strips 2. The feed is shorter when running strips through the die, thus reducing the time required 3. More blanks are produced per strip and fewer strips have to be handled.

3-13. STRIPS PER SHEET -WIDE RUN Now calculations are made to determine how many blanks are produced per sheet with the blanks positioned the wide way in the strip, and also how much waste is left.

3-14. STRIPS PER SHEET -NARROW RUN Next, we must know how many blanks are produced per sheet with the blanks positioned the narrow way in the strip. With blanks arranged the narrow way, more strips are cut from the sheet, but fewer blanks are contained in each strip.

THE MATERIAL STRIP

46

HOT ROLLED SHEETS Hot rolled sheets are formed easily. Low carbon sheets are used for tanks , barrels, pails, farm irnple·· rnents, lockers , cabinets, truck bodies, and other applications where scale and discoloration are not objectionable because surfaces are painted after forming. Hot rolled sheets are readily available in thicknesses ranging from #30 gage (0. 012) to #7 gage (0.1875).

Pickled and Oiled Sheets

A

STRIPS PER SHEET !.!?_ BLANKS PER S TR IP : §_Q BL A NKS PER SH E ET: 720 WASTE :

~4

FE E D

LL

W

~

0

b..o....Q

-~

I~:o_ 8

_____Jr

STRIPS PER SHEET 24 BLANKS PER STRIP . ;lQ BLA NKS PER SHEET720 WASTE : W. ~ 0 L. ~ 0

Fig. 3·15. Strip layouts for blanks run either the wide (A) or narrow (B) way.

Pickling, or the immersing of hot rolled sheets in acid solution, results in smooth, clean, scale-free surfaces having a uniform gray color. Oiling protects the surfaces against rust. These sheets are readily stamped or welded. Longlas ting painting or enameling is possible because of the absence of scale. Pickled and oiled sheets are used for household appliances, automotive parts, toys, and the like.

Copper Bearing Sheets Copper bearing sheets are hot rolled sheets having a 0.20 per cent minimum copper content. They are used for parts designed for outdoor exposure, or for indoor use under corrosive atmospheres. These sheets have a service life from 2 to 3 times longer than can be expected from non-copper bearing steels. They are used for roofing and siding, farm and industrial buildings, truck bodies , railroad cars, farm implements, signs, tanks, driers, ventilators, washing machines , and other similar applications.

Medium-Carbon Sheets

3-16. STRIPS At A is shown one of the strips ready to be fed through a die with blanks to be removed from it positione d the wide way. At B the blanks are positioned the narrow way. Five blanks are shown in each strip. Since they are run in cut off dies, no scrap bridge is produced.

~~ 0 ------------------~ A

~L¢================~

Hot rolled sheets having a 0.40 to 0. 50 per cent carbon content provide hardness, strength , and resistance to abrasion. They can be heat-treated to make the material even harder and stronger and are primarily used for scrapers, blades, hand tools, and the like.

COLD ROLLED SHEETS Cold rolled sheets have a smooth, de-oxidized satin finish which provides an excellent base for paint, lacquer, and enamel coating. Thicknesses are held to a high degree of accuracy. Cold rolled steel is produced by cold rolling hot rolled sheets to improve size and finish. Among many uses are included refrigerators, ranges, panels, lockers, and electrical fixtures.

B

Fig . 3· 16 . Strips ready for feeding either the wide (A) or narrow (B) woy.

MATERIALS Most starnpings are made of steel. Carbon content varies from S.A. E. 1010 to S.A.E. 1030 and therefore most blanks are in the ma chine or cold rolled steel range. Starnpin gs are also made from the following other rna terials: Aluminum Brass Bronze Copper Stainless steel Silicon steel Fiber Plastic sheet, etc.

3-17. DEFORMATION Six tempers of cold rolled steel sheets and strips are available and it is important to know exactly what operations can be performed on each. In the illustration: 1. Hard Hard sheets and strips will not bend in either direction of the grain without cracks or fracture. These tempers of steel are employed for flat blanks that require resistance to bending and wear. Direction of grain is shown alon'g lines A in the illustration. Rockwell hardness is B 90 to 100 2. Three-Quarter Hard This temper of steel will bend a total of 60 degrees from flat across the grain. This is shown as dimension B in the illustration. Hardness is Rockwell B 85 to 90

THE MATERIAL STRIP

47

Fig. 3·17. Var ious tempers of cold rolled steel from hard ( l) to dead soft (6) and kinds of deformation possible with each.

3. One-Half Hard This temper will bend to a sharp 90 degree an gle across the grain, shown as dimension C. Rockwell hardness is between B 70 and 85 4. One-Quarter Hard This commonly used temper of steel will bend over flat on itself across the grain and to a sharp rightan gle along the grain. Hardness is Rockwell B 60 to 70 S. Soft This temper will bend over flat upon itself both across the grain and along the grain. It is also used or moderate forming and drawing. Hardness is Rockwell B SO to 60 6. Dead Soft This temper of steel is used for deep drawing an d for severe bending and forming operations . Hardness is Rockwell B 40 to SO.

Finish Cold rolled steel is furnished in three grades of fi nish: 1. Dull Finish. This is a gray lustreless finish to which lacquer and paint bond well 2. Regular Bright Finish. This is a moderately bright finish suitable for most work. It is not recom:;Jended for plating unless buffed first 3. Best Bright Finish. This finish has a high lustre well suited for electroplating. It is the brightest finish obtainable.

Stretcher-Leveled Sheets These are cold rolled steel sheets that have been further processed by stretcher leveling and resquaring. They are used in the manufacture of metal furniture , table tops, truck body panels, partitions, and other equipment requiring perfectly flat material. Deep

Drawing Sheets

Deep drawing steel is prime quality cold rolled steel having a low carbon content. Sheets are thoroughly annealed, highly finished to a de-oxidized silver finish, and oiled. Deep drawing sheets are used for difficult drawing, spinning, and stamping operations such as automobile bodies, fenders, electrical fixtures, and laboratory equipment.

SILICON STEEL Also called electrical steel, silicon steel is extensively used for motors and generators. Lighter gages are suitable for transformers , reactors, relays, and other magnetic circuits.

3-18. SHEARED EDGES It now becomes necessary that you understand exactly what occurs when sheet material is cut between the cutting edges of a punch and die. This illustration shows the cut edge of a blank enlarged many times to reveal its contour. Observe the following:

THE MATERIAL STRIP

48 The top corner is defined by a small radius R. The size of this radius depends upon the thickness and hardness of the strip and on the sharpness of the punch and die members. A smooth, straight, burnished band goes around the periphery of the blank. The extent of this band, distance D, is approximately 1/ 3 the thickness T of the blank when the die is properly sharpened and when the correct clearance has been applied.

R

~)------

1'1'~ -:JL

Fig. 3-18. Enlarged view of sheared blank edge.

The remaining 2/ 3 of the edge is called the breakoff. The surface is somewhat rough and it tapers back slightly. Extent of the taper, distance B, is the amount of clearance between cutting edges. If burrs are produced in cutting the blanks they occur on this breakoff side of the blank. Burrs are produced when improper clearance has been applied and also when cutting edges become dull. The other side of the blank which has the radius and smooth, shiny band is called the burnished side of the blank. The location of the burnished side and of the burr side of the blank is very important for performing secondary operations such as shaving, burnishing, and the like. In addition, burr side position can influence the func tioni ng or the appearance of the finished stamping. In blanking the burnished band goes completely around the blank and the breakoff taper extends completely around the blank on the opposite side. This is not the case for blanks produced in cut off or progressive dies. In such dies , the burnished side may alternate from side to side in a number of positions and careful study is required to determine that any possible burr will not interfere wi th the function or appearance of the stamping. Shearing of material occurs in a continuous action. However, to understand the process i t will be necessary to "stop" the action in its various stages and to examine what occurs.

3-19. THEORY OF SHEAR 1. This illustration shows the cutting edges of a die with clearance C applied. The amount of this clearance is important as will be shown. 2. A material strip is introduced between the cutting edges and it is represented by phantom lines. Cutting a material strip occurs when it is sheared between cutting edges until the material between the edges has been compressed beyond its ultimate strength and fracture takes place. 3. The upper die begins its downward travel and the cutting edge of the punch penetrates the material by the amount A. The following stresses occur: The material in the radii at B is in tension, that is, it is stretched. The material between cutting edges, C, is compressed, or squeezed together. Stretching continues beyond the elastic limit of the material, then plastic deformation occurs. Observe that the same penetration and stretching is applied to both sides of the strip.

4. Continued descent of the upper cutting edge causes cracks to form in the material. These cleavage planes occur adjacent to the corner of each cutting edge. 5. Continued descent of the upper die causes the cracks to elongate until they meet. Here then is the reason for the importance of correct clearance. If the cracks fail to meet, a bad edge will be produced in the blank. 6. Further descent of the upper die causes the blank to separate from the strip. Separation occurs when the punch has penetrated approximately 1/ 3 of the strip. 7. Continued descent of the upper die causes the blank to be pushed into the die hole where it clings tightly because of the compressive stresses introduced prior to separation of the blank from the strip. In other words, the material at C in Step 3 was compressed and it acts like a compressed spring. The blank, confined in the die hole, tends to swell, but it is prevented fro m doing so by the confining walls of the die block. Conversely , the material around the punch tends to close in and therefore the strip clings tightly around the punch. 8. The punch has now penetrated entirely through the strip and the blank has been pushed entirely within the die hole. Observe that the edge of the blank and the edge of the strip have identical contours except that they are reversed. The strip will cling around the upper punch with approximately the same pressure as the blank clings within the die hole and a stripper will be required to remove it.

3-20. INSUFFICIENT CLEARANCE The inset at A shows the effects of insufficient clearance. There are four: a. Radius R is smaller than when correct clearance is applied b. A double burnished band Dis formed on the blank edge c. The breakoff angle B is smaller than when correct clearance is applied

THE MATERIAL STRIP

49

- -~-------

------F-2

----~·1_ _

.y---I

c

A

A

I

3

----~ Fig. 3-19. Enlarged views of clearance between cutting edges of a shearing die (1) and material undergoing shear (2 to 8).

THE MATERIAL STRIP

50

__ A· ---2

-· -

- - -2

3 Fig. 3·20. Enl ar ged vi ews of blank edge sheared with insufficient clearance (A) and materi al und ergo ing shear with insufficient clear· once ( 1 to 3).

d. Greater pressure is required for producing the blank. Referring to the illustration: 1. This shows cutting edges of a punch and die in partial penetration. It is obvious that the cracks that have appeared at the punch and die sides will not meet when extended because the clearance is insuffi. cient

Fig. 3·21. Enlarged views of blank edge sheared with excessive clearance (A) and material undergoing shear with excessive clear· once ( 1 to 3).

2. Continued downward descent of the punch causes elongation of the cracks. The uncut area between them will be broken in a secondary fracture 3. At the bottom of the stroke the secondary fracture has occurred and a second burnished band has been produced on the blank edge and on the strip edge. The characteristic contour shown in the inset at A has been formed.

51

TilE MATERIAL STRIP

3-21. EXCESSIVE CLEARANCE The inset at A shows the effects of excessive clearance. There are four: a. Radius R is considerably larger than when cor· rect clearance has been applied b. Burnished band Dis narrower c. The breakoff angle B is excessive d. A burr C is left on the blank. Referring to the illustration: 1. This shows cutting edges of a punch and die in partial penetration. Cracks have begun to form at opposite sides 2. Continued downward descent of the punch causes elongation and widening of the cracks. Their alignment is fairly good 3. At the bottom of the stroke, separation has occurred leaving the characteristic blank edges shown in he inset at A. When a die is provided with excessive clearance, less pressure is required to effect cutting of the material. For this reason, more clearance is often specified for blanking the heavy gages of stock to reduce pressure on the press.

3-22. EDGE CONTOUR The contour of the edge of a strip depends upon the process by which the strip is produced. Five contours may be recognized: 1. Strips produced in a shear have the burnished bands along the edges on opposite sides of the strip. If burrs are produced because of dull cutting edges, they will also occur on opposite sides of the strip. In addition, sheared strips often become spiraled or curved because the upper blade of the shear is at an angle to the lower blade. This makes the strips difficult to feed through the die unless they are first straightened 2. Strips produced in the slitter have the burnished bands on the same side of the strip. Blanks produced from these strips in cut off dies have a better appearance and they are fed more easily because they are straighter. Sheared strips or slit strips may be produced in the shear department of the plant, or they may be ordered directly from the mill. 3. Mill edge strips have a radius at each corner. They are produced by rolling sheared or slit strips at the mill. Mill edge strips are used for long stamp· ings such as handles, shelf brackets, and other parts where sharp edges would be objectionable .

2

3

4

5 Fig. 3-22. The various edge contours shown are the result of different production processes.

4. Rolled edge strips have a full radius at each side, rolled at the mill. They are used for parts where appearance is a decided factor such as ornamental grills, gratings, and the like . 5. Square edge strips are ordered from the mill when the sides ofthe strips must be square and smooth. The widths of these strips are held very accurately. Square edge strips are also specified when blanks are to be bent or formed edgewise. The square edges prevent cracking or splitting in the bending or forming operation.

Section 4

THE BLANK A blank is a piece of flat steel or other material cut to any outside contour. The thickness of a blank may range between 0.001 to 0.500 inch or more depending on its fu nction. However, most stampings are between 0.025 to 0.125 inch in thickness. Some blanks ha ve simple round, square, or rectangular contours. Others may be very irregular in shape. Many blanks are subsequently bent, formed, 1or drawn. It is important to realize, however, that when we refer to a blank, what is meant is the fla t part before any deformation has been applied.

Four advantages are realized when cut off dies are used: a . There is a minimum waste of material b. Cut off dies cost less to build c. Faster press speeds are possible d. There is no scrap strip to handle. After you have determined that a blank can be produced in a cut off operation, consider three additional factors before making a fina l decision: e. Accuracy in strip width. Sheared strips cannot be held to closer accuracy then ±0.010. If the width dimension between parallel sides of the blank must be held to closer limits, discard the idea of using a cut off die. f. Accuracy of the blank. If the blank must be held to close limits, it should be produced in a blanking die regardless of the number of strai ght sides that it may have. g. Flatness . If the part print contains the note , MUST BE FLAT, plan to design a blanking die because it will produce considerably flatter parts. Cut off dies produce blanks by a series of piercing, trimming, and cut off operations and uncut portions can become distorted, especially for heavier gages of strip. In blanking dies the en tire periphery is cut in one operation and distortion cannot occur . Blanking dies produce flat, accurate parts. Whatever accuracy has been "built in" the die is duplicated in the blanks and each is identical to every other blank that the die produces. This is true because the entire blank contour is cut and none of the edges of the strip form any edge of the blank . Blanking is the most widely used method of producing blanks from sheet materials. If the stampin g is intricate and it is to be produced complete in a progessive die, the contour of the blank may be formed by trimming away portions of the strip at one or more of the stations. 2. Siz e. Consider the size of the blank in relation to the number of parts required. This is especially important for large blanks because large dies are very costly to build . Determine if shearing and trimming would do the job, especially if production requirements are low. 3. Accuracy. Study the part print carefully to determine the degree of accuracy required in the blank. Very accurate blanks have to be produced in compound

4-1. TYPES OF BLANKS There are only two basic types of blanks: 1. Blanks having straight, parallel sides, two of whi ch are originally sides of the material strip . Small blanks of this type are produced in cut off dies. Large blanks are produced by square-shearing and trimming 2. Blanks having irregular contours cut entirely out of the material strip. When they are required in quantity, such blanks are produced in blanking dies . When only a few blanks are required, they may be shaped by contour sawing, nibbling, routing, or other machinin g operations.

l?l lJ -~ -

0

eva

2

Fi g. 4·1 . Two basic types of blank s.

To select the best meth od of producing a particular blank, consider fi ve factors : 1. Contour. If the blank has two parallel sides , determine if it can be produced in a cut off operation . The width between the parallel sides would then become the width of the strip.

52

53

THE BLANK

dies in which all operations are performed simultaneously at one station. Blanks requiring a lesser degree of accuracy may be produced in more economical twostation dies. 4. Number required. This information is taken from the design order and it often determines the type of di e to be designed as well as the class of die. 5. Burr side. The burr side must be known when blanks are to be shaved or burnished in a subsequent operation. The same applies for blanks that are to be a ssembled into other components and those that are to bave components assembled into them. The presence of burrs at engaging edges can slow down assembly operations considerably.

PRODUCING BLANKS Let us now gain an understanding of the various ::nethods of producing blanks. We will begin by consider. g ways in which blanks may be shaped without the s e of dies . These low-cost, but relatively slow methods are employed when only a few blanks are required and · would be uneconomical to design and build special ies for producing them .

Circle Shearing Large, round blanks may be circle-sheared when uantities required are moderate . Square blanks are clamped in the center of a circle shearing machine, Two disk-shaped cutters are adjusted to the required ra dius and they apply rotation to the blank and at the same time cut it to circular shape. For larger quantities it is less expensive to order round blanks precut to the required diameter. Steel companies stock various sizes of round blanks, or they can supply them cut to special sizes .

Contour Sawing When only a few blanks are required, their contours :nay be laid out directly on sheet material. After lines have been scribed , the blanks are sawed out in a metalcutting handsaw. For contour sawing a number of bl anks requiring greater accuracy, a short stack of square or rectangular blanks are clamped in a vise and tack welded together at several places around the edges. The outline of the blank is laid out on the pper sheet and the blanks are sawed directly to this ou tline. Thus, all the blanks are identical in contour.

Nibbling The nibbling machine operates by reciprocating a up and down at about five strokes per second. Th e punch is provided with a pilot long enough so it is ::wt raised above the material being cut. As the sheet is moved, the punch cuts a series of partial holes :hat overlap each other. A jagged edge is left around :he edges of the blank and the sharp corners left by die punch must be die-filed after the nibbling operation. f course, the nibbling process is used to produce ~ anks when only one, two, or a few are required . ~unch

Routing A routing machine is provided with a long radial arm which can travel over a large area . Mounted at the outer end of the arm is a rapidly revolving cutting tool similar to an end-mill cutter which can cut its way through a stack of blanks . The router bit, as the cutting tool is called, rotates at about 15,000 revolutions per minute and it is guided by a template to produce blanks identical to the template. Routing large aluminum blanks is common practice in the aircraft and missile industries .

Flame Cutting Flame cutting or torch cutting means the cutting of thick blanks by the use of an acetylene torch. In operation, the torch heats the metal under its flame tip until it melts. Compressed air then blows the molten metal out, forming a narrow channel called the kerf. The width of the kerf ranges from 5/ 64 inch to 1/ 8 inch depending upon stock thickness and the speed of the torch. For producing thick blanks in quantity, a template guides the torch by means of a pantograph. Flame cutting is employed for cutting blanks ranging from \4 to 1 inch or more in thickness. Holes in blanks can also be torch cut by the same method. Flame cutting leaves the edges somewhat rough and ridged. However, such edges are satisfactory for some parts for trucks, tanks, ships , and other similar applications.

4-2. SQUARE SHEARING Large, straight-sided blanks are produced in the shear by cutting sheets into strips, then cutting the strips to requi red lengths or widths . Blanks larger than 8 by 10 inches and composed primarily of straight sides are ordinarily produced by shearing because of the high cost of large dies . Blanks cut in a modern shear can be held to an accuracy of 0.005. Four factors govern shearing accuracy: 1. The shear must have sufficient rigidity to withstand the cutting load without deflection or spring. 2. Knife clearance must be set correctly and proper rake selected to reduce twist, camber , or bow. Rake is the angle of the upper knife in relation to the horizontal lower knife of the shear. Twist is spiraling of the strip and it is more severe in soft, narrow, or thick strips than it is in hard, wide, or thin strips. Camber is curvature along the edge in the plane of the strip. Bow is curvature perpendicular to the surface of the strip. 3. Good gaging practice must be followed. 4. The sheet must be held down securely while shearing occurs.

In the upper iII us trati on: For producing square and rectangular blanks shown in the upper inset, the sheet is first cut into strips to length A of the blanks. The strips are then run through

THE BLANK

54

the shear again and cut into blanks having width B. Here is the method of listing operations on the route sheet: Operation No. 1. Shear to length. (A) Operation No. 2. Shear to width. (B)

In the lower illustration: When the grain of the material must run lengthwise of the blank for extra stiffness, the sheet is cut into strips to width B of the blanks. The strips are then run through the shear again and cut into blanks having length A. On the route sheet, operations are listed as follows: Operation No. 1. Shear to width. (B) Operation No. 2. Shear to Length . (A)

r A

I L~..-__l,

_ _ __ J

~B _j

®

Ll I @ ~ A _j Fig. 4· 2. Rec tangular blanks sheared from wide and narrow strips.

fig. 4·3. Triangular blank s made by shearing rectangular blanks sheared from wide and narrow strips.

[1/1 I-s~

4·3. TRIANGULAR BLANKS T rian gu ar bl anks are produced by shearing square or rec tangula r blanks, then splitting them to produce two blanks. In the upper illustration: Operati on o. 1. Shear to length. (A) Operation o. 2. Shear to double width. (B) Operation o. 3. Split. (C) Note th at alth ough operation No. 2 states "Shear to double width" , this do es not mean that the strip is to be cut twice the wid th of a single blank. It simply means that the s quare ,or rectangular blanks are to be made wide enough s o s plittin g will produce two full blanks .

fr:\LLZ I ~ ~A__j

l

In the lower illustration: For running strips the na rrow way, operations are listed as follows: Operation No. 1. Shear to width. ( B) Operation No. 2. Shear to double length . (A) Operation No. 3. Split. (C)

Fig. 4·4. Angular edge blanks made by shearing rectangular blank s sh eared from wide and narrow strips.

55

TIIE BLANK

4-4. ANGULAR EDGE BLANKS

4-6. PARALLELOGRAMS

Wider blanks having one angular edge can be pro.=uc ed by the same method employed for triangular anks. For the upper illustration: Operation No . 1. Shear to length . (A) Operation No. 2. Shear to double width . (B) Operation No. 3. Split. (C)

Blanks in the shape of an angular parallelogram are produced by shearing with the strip positioned at an angle to the shear blade. For the wide strips, upper illustration: Operation No. 1. Shear to length. (A) Operation No. 2. Shear to width. (B) For narrow strips, lower illustration:

the lower illustration:

The function run them the : :lows: Ope ration No. Operation No . Operation No.

of some blanks renders it necessary narrow way. Operations are then as

Operation No. 1. Shear to width. (B) Operation No. 2. Shear to length. (A)

1. Shear to width. (B) 2. Shear to double length . (A) 3. Split. (C)

..t-5. ADDED CUTS One or more extra cuts may be required to complete ::.:e blanks. Here is the order of operations for the blank - th e upper inset: Operation No. 1. Shear to length, (A) Operation No. 2. Shear to double width . (B) Operation No . 3. Split. (C) Operation No. 4. Trim. (D) In the lower iII ustration:

Operation Operation Operation Operation

No. No. No. No.

1. 2. 3. 4.

Shear Shear Split. Trim .

to width. (B) to double length. (A)

(C) (0) Fig. 4·6. Parallelogram narrow strips.

shaped

blanks

sheared from wide and

4·7. TRIANGULAR BLANKS

~1 71

~B~

Triangular blanks with an acute angle at each of the three apexes are produced by splitting a parallelogram. For wide strips:

Operation No. 1. Shear to length. (A) Operation No. 2. Shear to double width. (B) Operation No. 3. Split. (C) For narrow strips:

Operation No. 1. Shear to width. (B) Operation No. 2. Shear to double length (A) Operation No. 3. Split. (C)

4-8. TRAPEZOIDAL BLANKS Large trapezoidal blanks are produced by employing the same method. For wide strips:

Operation No. 1. Shear to length. (A) Operation No. 2. Shear to double width. (B) Operation No. 3. Split. (C) For narrow strips:

=;. 4·5.

Blanks produced by added cutting of angular edge pieces.

Operation No. 1. Shear to width. (B) Operation No. 2. Shear to double length. (A) Operation No. 3. Split. (C)

THE BLANK

56

4-9. ADDEO CUTS One or more extra cuts may be required to complete the blanks. For wide strips:


No. No . No. No.

1. Shear to length. (A) 2. Shear to double width. (B) 3. Split. (C) 4. Trim. (D)

For narrow strips:


No. No. No. No.

1. Shear to width. (B) 2. Shear to double length . (A) 3. Split. (C) 4. Trim. (D)

LV\ I ~ B____j

Fig. 4·7. Acute-angle triangular blanks made by shearing parallel· ogram shaped blanks sheared from wide and narrow strips.

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v~·~

Fig. 4·9. Blanks produced by add ed cutting of tr apezoida l blanks.

4-10. NOTCHING

fn\[V \ I \!:!) ~ ._j Fig. 4-8. Trapezoidal blanks are sheared in a manner similar to acute-angle triangular blanks.

Irregular notches or cuts are applied in trimming dies after the straight sides of the blanks have been sheared. It is less expensive to design and build a die for trimming small portions of a blank than it would be to design and build a die for producing the entire blank. This is because the length of cutting edges is shorter for trimming than for blanking and less fitting is required. Also, less material is required in the strip when blanks are sheared because there is no scrap bridge. In this connection , you should know exactly what is meant by the words "notching" and "trimming" , Notching is the operation of cutting small portions from the edges of a strip or blank. The area of such portions is no greater than that of average pierced holes. Trimming means the removal of larger portions of metal to alter the form in the area of the trimmed

THE BLANK

57

1cl

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; ig. 4-10. Blanks sheared and trimmed from wide and narrow strips.

Fig. 4-11. Blanks she ared and pierced from wid e and narrow strips.

ro ntour. The difference is one of degree. Trimming -· us means the reshaping of blanks on a larger scale :il an is accomplished by simple notching.

applied to it and the amount of resistance is called the shear strength. To effect cutting, the shear stress applied to the material must be greater than the shear strength . The molecular structure will then fail and fracture and separation will occur.

In the illustration, operations for wide strips are:

Operation No. 1. Shear to length. (A) Operation No. 2. Shear to width. (B) Operation No. 3. Trim. (C) -or narrow strips:

Operation No. 1. Shear to width. (B) Operation No. 2. Shear to length. (A) Operation No. 3. Trim. (C)

-11. PIERCING Holes may be pierced in the blanks in a turret punch -h en required quantities are low. For greater pro:: ction, a special piercing die is designed and built : r the job. After they have been sheared, the blanks are .::and-fed into the piercing die. perations for wide strips are: Operation No. 1. Shear to length. (A)

Operation No. 2. Shear to width . (B) Operation No. 3. Pierce. (C) -or narrow strips:

Shear strengths of various materials have been found by experiment and they are listed in the table. The shear strength A is equivalent to the force required to cut a bar one inch square in two and these are the values given. Expressed differently, the shear strength values in the table are a measure of the force required to cut an area one inch square . Given this information it is a simple matter to determine the shear strength for any area to be cut.

4-13. AREA TO BE CUT The first step in establishing cutting force or blanking force is to determine the area to be cut. For straight cuts as performed in shearing and in some cut off die operations, the area to be cut is found by multiplying the length by the thickness. Formula: Area = L x T

Operation No. l.1Shear to width. (B) Operation No. 2. Shear to length. (A) Operation No. 3. Pierce. (C)

4-14. AREA TO BE CUT IN BLANKING -12. SHEAR STRENGTH In cutting any material, a force acting on the area be sheared (called the shear stress) is applied to ' e material. The material offers resistance to separaLion. Its molecular structure resists the shear stress ~o

In blanking, an area is removed from within the strip and the cut is therefore around an enclosed contour. The area to be cut is found by multiplying the perimeter of the blank by the thickness. For round cuts:

Area = D x 3.1416 x T

For rectangular cuts: Area = (2L + 2W)

x

T

.

58

THE BLANK

MATERIAL

SHEAR

STRE~GTH

Pounds per square inch

A

STEEL.lO% carbon content

Hot Rolled - 35, 000 Gold Rolled 45' 000

STEEL. 20% c arbon content

Hot Rolled - 45 , 000 Cold Rolled 55' 000

STEEL .JO% carbon cont ent

Ho t Rolled Co l d Rolled

STA INLESS STEEL

60' 000

SU.ICON STEEL

65' 000

TIN

5 ' 000

AL UMINUM

A

55 , 000 65,000

10 , 00 0

COPPER

25' 000

BRASS

J 0 ' 000

BRONZE

35,000

Fig. 4-12. Drawing which illustrates shear strength an d table of shear strengths for various materials.

We are now prepared consider the formula for deterdetermining the blanking force. Blanking force

=S x P x T

In which: S = Shear strength as taken from the table in Fig. 4-12. P ::: Perimeter. This is the distance around all cut edges. T = Thickness of material to be cut. For example, a blank 2 inches by 4 inches is to be cut in a strip of No . 16 gage (0. 0598 inch thick), 0. 20 per cent carbon, cold rolled steel. In addition, two \6 inch holes are to be pierced in a previous station, piercing of the holes to occur simultaneously with blanking of the part. Perimeter of blank (2 + 2 + 4+ 4) = 12 inches Perimeter of holes (2 x 0.500 x 3.1416) = 3. 1416 inches 15.1416 inches Formula: 55,000 x 15.1416 x 0.0598 =49,800.722 lbs. Since press capacities are rated in tons, this number is divided by 2,000 = 24.9 tons. A thirty ton press would be selected . \\'hen cutting faces of the punch or die block are ground at an angle so that cutting of the periphery of the blank occu rs gradually, the shear strength values given in Fig. 4-12 may be reduced by one -half. This is called "shearing" the die and the operation will be explained in Section 7, "How to Design Die Blocks," and also in Section 8, "How to Design Blanki ng Pun ches."

Fig . 4-13. Dra wing which illustrate s area subj ected to shear.

Fig· 4-14. Drawing which illustrates areas subjected to shear in blanking.

Section 5

FOURTEEN STEPS TO DESIGN A DIE \Ve have completed the introductory portion of our -ork and we must now come to an understanding of die :!esign itself, of the procedure followed by a die de- igner in organizing components of different shapes, si zes, and composition into the unified concept called a die. First, it should be understood that a definite -der of steps must be taken in originating any die :.esign.

the strip with the blank and pierced slugs pushed out of it is shown between views. This is the way the strip would be visualized before drawing th e actual views. To improve your own faculty of visualization, make a free-hand pictorial sketch of the strip on a separate sheet. In Section 6, many rules for laying out scrap strips properly will be given and methods of checking and verifying designs will be explained.

Haphazard design methods waste time and they en result in inefficient press tools, but systematic ]iOcedures will provide: 1. Consistently good designs 2. Speedy, effortless work 3. Fewer erasures 4. Improved appearance of drawings 5. Stronger punch and die components. In this section are illustrated the fourteen steps :equired for designing a die for making the repres entative part shown in the print of the link, Fig. 1-7. Study this order of steps carefully because , by :allowing it closely, you can begin at once to design a :::ie yourself and when you have completed your design , e results you have achieved will surprise and please

In sections which follow in this book, will be explained in far greater detail. As each section, keep referring back to the list in this section to fix the position of firmly in your mind.

each step you study illustrated each step

5-1. THE SCRAP STRIP The first step in designing any die is to lay out the material strip exactly as it will appear at the bottom of the press stroke . Three views are shown, and the distance between views must be carefully estimated to prevent views from running into each other as the die grows. Always use red lead when drawing the material strip so it will show clearly through the maze of black lines which will represent the punch and die members.

5-2. THE DIE BLOCK

By appropriate substitutions the same steps can be ~ak en in the design of any die. For example, in design:_:Jg a multiple-station progressive die, all die blocks Tould be laid out at Step 2, The Die Block, If a spring s ripper must be employed because of the nature of the !)eration it simply replaces the solid stripper at Step : 0, "The Stripper Plate". the top view, the outlines of the strip and of all ::.oles or openings are drawn with thin, red phantom :in es. In the front and side view, the strip thickness :s filled in solid red. The blank and slugs are shown shed out of the strip and they are also drawn solid ;ed. Locate their top surfaces in line, or flush, with :.1e bottom surface of the strip . A pictorial drawing of

Draw the three views of the die block. In the top view, the die block usually is rectangular in shape. The blank opening and holes for punches are represented by black lines. Simply draw with black lead directly over the red lines. Dotted lines represent edges at the bottoms of blank and slug openings . These are larger because of tapered walls provided for blank and slug relief. Leave sufficient room for the screws and dowels which will fasten the block to the die set. Because both the front and side views will be section views, the lines representing internal openings are solid lines. The pictorial drawing now shows the die block in position under the strip.

59

FOUR TEEN STEPS TO DESIGN A DIE

60

I

--

-

Fi g. 5·1. Material strip as it appear s at th e bottom of th e press stroke.

I

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1

Fig. 5· 2. Vario us vi ews of the die bl o, k an d material strip.

+ I

I

FOURTEEN STEPS TO DESIGN A DIE

61

I

Et

I +~

I

Fig. 5·3. Various views of the die assembly with the blanking punch added.

5·3. THE BLANKING PUNCH The blanking punch is now drawn in position above the die block . Its plan view is applied in the upper right corner in an inverted position. That is, the punch is drawn as if removed from above the die block and turned over so cutting edges are viewed directly. When outlining the flange width and thickness, take into consideration the screws and dowels which will fasten it to the punch holder of the die set. In the lower section views, the cutting face of the blanking punch is drawn flus h with the top of the die block with a single line. To improve your ability to visualize the die in three dimen sions, turn to the pictorial drawing and sketch the blanking punch above the blank opening in the die block .

\,-____


62

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Fig. 5·4. Various views of the die assembly with the pie rci ng punches added.

5·4. PIERCING PUNCHES Piercing punches are now drawn in their proper positions. Include their plan views , represented by concentric circles, in the upper-right corner, remembering that this view of the piercing punches and blanking punch is opposite from the plan view of the die block. The finished die will appear as if opened, much in the same manner as a book is opened. Sketch piercing punches on the pictorial drawing .

FOURTEEN STEPS TO DESIGN A DI E

I

IJY I

~J

I

t I

Fig. 5-5. Various views of the die assembly with the punch plate added.

5-S. PUNCH PLATE In this step, the punch plate which retains the piercing punches is drawn in the front and upper-right views. This plate is usually made of a good grade of machine steel. Here again, room must be provided for the screws and dowels which will secure it to the punch holder of the die set.

63


64

Yl ~I

I

t

Fig. 5·6. Various views of the die assembly with the pilots added.

5-6. PILOTS Insert the pilots that will accurately locate the strip, as well as the nuts that hold them in the blanking punch. Only outlines of the parts are drawn , Section lines are not applied until the entire design is completed. Be sure to draw the concentric circles to represent pilots and pilot nuts in the upper-right view in addition to showing them in the front view.

?OURTEEN STEPS TO DESIGN A DIE

: I

!Y~ [fll

65

l I

~ ~o:IF==IIc" i

\A

Fig. 5-7. Variou s views of the die assembly with the back gage and front spacer add ed .

5·7. GAGES Until now , the strip has not been located in any way. It simply lies on top of the die block. So now apply the back gage and front spacer which guide the strip at its sides. Strip support A, if one is used, can be drawn in at this time. In the front and side views, draw horizonta l lines to represent the top and bottom surfaces of the punch holder and die holder of the die set. Thicknesses are taken from a die set catalog. For a small die such as this one, a punch holder 1~ inches thick and a die holder 1~ inches thick are usually selected.

66


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if

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Fig, 5·8. Various views of the die assembly with the finger stop added.

5-8.

FI~GER

STOP

Although the strip is now supported sideways between the back gage and front spacer, no provision has been made for endwise location. So draw a finger stop, which initially stops the strip for piercing the two holes in the first blank. In operation , the finger stop is pushed in and the end of the strip engages its toe. After the press has been tripped to pierce the holes, the strip is then advanced until its end contacts the automatic stop. Also at this time the punch shank is drawn in the upper right-hand view; being represented by a dotted circle. It should be so placed that any clearance hole will appear entirely within , or completely outsi de of it.


:I

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67

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Fig. 5-9. Various views of the die assembly with the automatic stop added.

-9 . AUTOMATIC STOP An automatic stop, which locates the strip at every

:

ch stroke, is now drawn. There are numerous types automatic stops, but the one illustrated is perhaps :.:.e most widely used. In operation, the end of the strip acts the toe of the stop moving it to a "set" ;c::sHion . When the press ram descends, a square-head :=: screw, retained in the punch holder, contacts the -=- site end of the stop causing the toe to be raised - ve the strip. A spring then "triggers" the stop ::21sing it to rotate a few degrees so that the toe of the ~

stop comes to a position above the scrap bridge. When the ram goes up, the stop toe falls on top ofthe scrap bridge, allowing the strip to slide under it until the toe of the stop falls into the blanked opening. Travel continues until the right edge of the blanked opening contacts the toe, moving it and "resetting" the stop . These motions take place at high speeds, much faster than the time it takes to describe them. Of course, all lines have been drawn very lightly so far for easy erasure when sizes of components are altered.

68

FOURTE EN STEP S TO DESIGN A DI E

Fig. 5·10. Various views of the die assembly with the stripper added.

5-10. STRIPPER The stripper is now applied to all three views. Strippers remove the strip from around blanking and piercing punches. For some types of dies, a knockout would be designed at this step. Knockouts are internal strippers and they remove blanks and formed parts from inside cavities of punches and dies. In the upper-left plan view of the die block, all lines under the solid stripper now become dotted lines since they now represent hidden edges of surfaces. A stripper is required because material strip always clings very tightly around any punch which penetrates it and some provision must be made to remove it.

FOURT EEN STEPS TO DESIGN A· DIE

~

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11'

~

: ~ I~

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69

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Fig. 5·11. Var ious views of the. die assembly with the fasteners added.

5-11. FASTENERS In this s tep, screws, dowels, and other fasteners are drawn . For press tools, all dowels are the same diameter as the screws for any particular member. Note that button-head socket screws are employed to fasten the solid s tripper to the die block. Because of their low head height, strength, and clean lines, these are excellent fasteners for this application . Considerable designing ability is required for applying fasteners properly and there are a number of rules to be learned . This subject will be taken up in detail in Section 16, "How to Apply Fasteners."

70


Fig. 5·12. Various views of the die assembly including the die set.

5-12. THE DIE SET The die set, which was started with horizontal lines in the lower views of Step 7, and with a dotted circle in the upper-right view of Step 8, is now completed. To draw in the die set before this step will very frequently result in considerable erasing when die sections are found to be too small and their sizes are increased. Die sets are available in a bewildering variety of shapes and sizes, and judgement must be exercised for selecting a suitable one under given conditions. In addition, a definite method of procedure must be followed in applying the views to the drawing. This subject will be explained thoroughly in Section 17, "How to Select a Die Set."

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c r>.> . No- O SO S - 1'\\ I 1 ~'2. ~•A· SHANK 3/E\R\V\. \1-\R\.1 ~ 1' - -,.._~

S. i '<:'£ \.. S\-\L':>. 'e.\J S \-'. •

I DIA."5 POS:.TS

t>.SS'V

b R.,

8

'3/e, RM. 'THRU ""\ H\..'S ~ "P-.~.

c 'e.:.ol=\.'E'_ , t i·/loo.P

fOR ~1& - \b S O C·

cr""p

~-P~

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"''

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'14- - '20 \I>.? 'TI-\R\.1

11'4 RM· \1-\RU

S £C. T I 0 N

ffi.. - .i.A.

P . 'i'

:?>te - <{, "TAP

S.~C\IC>N

IB- JB

"-

Fig. 5-13. Various views of the complete die with d i mensions and notes.

TI-IRU

C 'BOI'.C. FOR ~/e, SOC .CAP. $Ct;:t. \-\ L S,

""'

72



73

5-13. DIMENSIONS AND NOTES

5-14. BILL OF MATERIAL

All dimensions and notes are now lettered in place. Die block dimensions are applied as for a jig borer layout. All information that the die maker might require to complete the die should now be on the drawing, unless components are detailed separately as is done for more complex dies.

The final step in designing this die is to fill in the bill of material. This lists all components which will enter into building the die. Unless printed sheets are used, the border is app lied, the paper is trimmed, and the die design is complete. Each of the fourteen steps will now be taken up in detail.

Section 6

HOW TO LAY OUT A SCRAP STRIP itself. In fact, the scrap strip layout will govern the shapes and sizes of many of the die members.

The first step in designing a die is to lay out the material strip exactly as it will appear after all operations have been performed on it. It is then called a scrap strip. To be successful, scrap strip desi gning must follow a definite procedure which will insure that nothing has been omitted or left to chance . Fifty to seventy per cent of the cost of a stamping is for material. Therefore, the method employed for laying out the scrap strip directly influences the financial success or failure of any press operation. The blank must be positioned so a maximum area of the strip is utilized in production of the stamping. This blank layout is drawn before any work is done on the die design

6-1. SCRA P STRIPS Illustrated are nine representative scrap strips for different stampings. These are photographs of actual strips of metal as removed from dies and they reveal the progression of steps taken in producing the fin· ished parts. In designing a scrap st rip on paper, it is necessary to lay out the contours of outside edges and openings exactly as they will appear in the finishe d metal strips. Following are the names of the various parts shown:

5

4

6

7

9

8 B. Jahn Mfg. Co. Fig. 6· 1. Representative scrap strips.

74

HOW TO LAY OUT A SCRAP STRIP

75

1 . Part for lock 2. Toe plate for _roller skates 3. Key levers 4. Wall bracket 5. Fluid drive coupler 6. Shell for radio loud speaker 7. Fruit parer 8. Camera side plate 9. Automobile radiator cap. In illustrations to follow, we will consider the steps taken in designing a scrap strip for a pierced ink - from the first tentative tries to the finished layout. The same steps applied to the design of a scrap st rip for any similar part should assure successful results . This section of the book further explains Step 1 in ec tion 5, "Fourteen Steps to Design a Die".

6-2. BASIC BLANK SHAPES The shape of most blanks will fall into one of the classifications shown here. Accompanying scrap strip es igns for these representative part outlines provide a basis for establishing the correct material layout for any similar part to be blanked. As shown, the scrap s trip for a circular blank is laid out fo r a double row. This is more economical than a single-row layout and it is usually specified for such dies except those for arge blanks and for low production. Many blanks have ·elaborate contours that cannot be ~e adily classified. Upon study, these will be found to Je made up of two or more of the basi c forms illusrated , and scrap strips for these must take into consi de ration the particular shape combination.

dJ v[[] .J11?81? W~rw. . i

0 0 o o j

CIRCULAR

\! IVD\71 ,..~,.

~

..

lOGO }

PARTIAL Ff tNG

~ IDDD! RECTANGULA R AND SQUARE

~

methods. In the first case the blank~ are arranged in a single row and the strip is passed through the die once to cut all blanks from it. At A, the parts are located in a vertical position in the strip. This is the preferred . method because the maximum number of blanks can be cut from one strip and fewer strips must be handled. When severe bends are required in subsequent operations, as in flat springs made from strip, method B must be used. This procedure involves handling more strips to produce the same number of blanks. The shape of the part will often lend itself to angu· lar positioning, as at C. For some contours, this method is economical of material. Also, it has the further advantage of allowing bends to be made without possible fracture. Material can be saved by the 11 single-run, two pass" method (0, E, and F) when employed for certain part shapes. In this case , the blank s are positioned in the strip in a sin gle row . Alternate blanks are turned upside down as shown, and the strip must be passed through the die twice to remove all blanks from it. As the strip goes through the fi rst time , the blanks in the upper row are cut. The strip is then turned over and run throu gh the die again, removing the rest of the blanks . A ten to fifteen per cent higher labor cost will occur in double-run layouts. The operator must pass the strip through the die twice and emp loy greater care in gaging it. Extra labor cost is offset by the saving in material when blanks are large and waste is considerable. Vertical positioning is shown at D, horizontal positioning at E, and angular positioning at F. The contour and bends found in many parts will dictate use of angular positioning. SINGLE- ROW MATERIAL LA'!'(}UTS

T>= PE A= - - - >

ICSlJCSl1l " L' SHAPE

'

~p~[

lU l l~

"u" SHA PE

Fig. 6-3. Vari ous ways in which blanks can be positioned. Fig. 6-2. Basic blan k shapes.

6-3. BLANK POSITIONING

6-4. DOUBLE-ROW LAYOUTS

Blanks can be positioned eleven different ways in · e strip. Choice of the correct method depends upon ~ rt shape, production requirements , and any bends at must be applied. The illustration shows the " si ngle-row, one pass," and 11 single-row, two pass"

Further economy in material can be achieved by use of Hdouble-row, two pass" layouts shown at A and B. The strip is run through the die twice as in previous examples, but blanking centers are closer together, giving greater operating speed .

76


The same positioning method may be used for double row gang dies C and D. An extra punch and die opening is applied to the die , cutting two blanks with each stroke , and the s trip is run through only once. Gang dies are hi gh-speed tools and the method should be selected only when the added expense of the extra punch and die hole is warranted. TWO PASSES

::~

,. -

c..:Pl.=.ERc:..:C=.=E,_-_,2'--'H-'-'L'-"' 'S

I R

ONE PASS

-11--"'16 GA. (0625 ) C .R.S.

A

Fig. 6-6. Typical part print.

6-7. PART LAYOUT

Slloded u~Ms rttY...ISMJJ IJURChts

The fi rst step is to lay out the part accurately on paper. Check dimensions carefully at this time, as any mis take will result in considerable useless work .

Fig. 6·4. Double-row blank layouts.

6·5. TRIPLE-ROW LAYOUTS Illustrated here are two triple-row gang dies of the progressive type. At A is the layout for a die used to produce washers at high speed , while at B is shown a die to produce elliptical blanks . Such dies may have more than three rows; the number is limited only by press size and production requirements .

0 Fig. 6-7. Part layout on paper.

6·8. WIDE RUN POSITIONING Usually, the first thought that comes to mind is to lay out the blanks , side by side, as shown at A. Blanks arranged in this manner can be run through the die in any of four different ways, shown further at B, C, and D. It i s obvious that this layout is wasteful of material.

A

A

c

8

0

B

Fig . 6·5. Tr iple row blank layout s. Fig. 6·8. Part positioned for wide run.

6-6. PART PRINT A scrap strip is to be desi gned for producing small, elbow-shaped parts c alled Offset Links . Study of the part print shows that dimens ional allowances are liberal enough so a two-st ation progressive die can be used, instead of a compound dk In such dies the holes are pierced at one station and the part is bl anked out at the succeeding gtation.

6·9. NARROW RUN POSITIONING If a bend were to be applied to the long arm of this part, the fi rst thought would be to lay it out the narrow way, as shown, because bends should be made across the grai n, preferably. However, this layout is also wasteful of material. Again, it is possible to run the strip in four ways.

77


6-11. NESTING To summarize: a. The side-by-size layouts, except for some rectangular or round parts, are wasteful of material. b. Double-run layouts can be a source of trouble and they are seldom used for small parts. Only for very large blanks are the savings in material great enough to justify their use . c. Double-die layouts are quite expensive except for extremely large quantities.

I PPP I ~----~ ---- -- -- -----,

I I

I

Fig. 6·9. Part positioned for narro w run .

6-10. DOUBLE ROW LAYOUTS Double-row layouts are economical of material , but they may lure the designer into trouble. At A, this tJart is shown in a wide-run , double-row layout.. With . o. 1 the blanking station , the strip would be run du ough, blanking all holes in the upper portion of the s ri p. It would then be reversed and run through the die a second time. Actually, in running the strip for the fi rst row, it becomes curved and distorted, and this can cause it to stick and bind when running the second :ime. In fact, there is a ten to fifteen per cent increase in labor cost for double-row dies. Double die layouts, ·n which both No's 1 and 2 would be blanking stations, resent fewer difficulties. But few parts have the high~roduction requirements which would justify the expen~e of providing two blanking punches and die openings, an d an extra set of piercing punches. A double-row, narrow-run layout is shown at B. This can be either a two-pass layout, in which the strip .is run through rh e die twice to extract all blanks, or it can be a double die layout, with both No's 1 and 2 the blanking stations.

I

I

Fig. 6·11. Tr acing another part layout from Fig. 6-7.

Mast blanks with irregular contours will nest (fit snugly one against another) when placed side by side in the correct position. The best nesting position for the particular part must be found before proceeding with the strip layout. Here is the method to follow: Over the part layout shown in Fig. 6-7 , place a sheet of thin , translucent paper and trace the part outline .

6-12. NESTING POSITION Move the paper over the blank layout until the best nesting position is found. Shown here is the best nesting position for this part. Correct scrap bridge allowances must be allowed between blanks as will be explained later.

6-13. CORRECTING THE LAYOUT Fasten this layout to the drafting table, straighten inaccurate lines , and check dimensions. Draw guide lines A and, leaving the correct scrap bridge allowance, part line B of the next blank to help in positioning the paper for tracing it.

Fig. 6·10. Double-row layouts.

6-14. DRAWING THE THIRD BLANK Place the sheet back .over the part layout shown in Fig. 6-7, and draw the third blank as accurately as possible.

78


6·15. COMPLETED LAYOUT

- - - ------------,

The blank layout is now complete and accurate. It might appear that our task "is finished, but much work remains to be done before we can be sure that we have the best possible layout. We must know that it wil1 per· form satisfactorily.

I

I I

I I I

I I I I

L_----".--- ----

--~---~

Fig. 6-12. Moving the tracing to the best nesting position.

Fig. 6-15. Comp leted layout.

6-16. RUNNING THE STRIP There are four ways of running the strip through the die, using the layout just completed. Numbered 1, 2, 3, and 4, one of these will be the best method for a given part, depending on its contour. From the layout in Fig. 6-15, it is possible to trace directly for all four me· thods of running the strip.

Fig. 6-13. Corrected layout .

.------/-------- - - ' - - - -

Fig. 6-14. Drawing the third blank.

Fig. 6·16. Four ways in which the strip may be run through the die.

SO W TO LAY OUT A SCRAP STRIP

79

( Fig. 6·17. Ways of rotating the strip to obtain the various running methods.

6·17. ROTATING THE STRIP Method number 2 of running the strip is arrived at · r turning around strip number 1 as shown, and tracing ~- in position. Method number 3 is arrived at by turning -:rip number 1 upside down as shown, and tracing it :..:~ this position. Method number 4 of running the strip ;- arrived at by turning strip number 3 around as :;.Jown, and tracing it in this position.

From it, it is possible to trace directly for all four methods of running the strip, shown in Fig. 6-16.

A

6-1 8. PIERCE AND BLANK LAYOUTS The strip laid out in Fig. 6-15 is used in making punch and blanking punch layouts. At A is a ...a_•out which corresponds to method number 4, Fig. :- 6. At B the layout corresponds to method number 3. ? te rcing punches are usually drawn solid black. (White · ere for convenience .) Circles C are pilots in the ::..anking punch, used to locate the strip prior to blank- a . These are drawn solid red. This show s the import~c e of drawing three bl anks in the layout in Fig. 6-15. ~:ercing

8

Fi g. 6·18. Use of th e layout for making the pi ercing and blanking punc h Iayout.


80

6-19. TRACING PIERCE AND BLANK LAYOUTS Four piercing punch and blanking punch layouts are traced from the layout in Fig. 6-15 to correspond to the four methods of running the strip. The line above each of these represents the front edge of the back gage against which the strip is positioned in its travel through the die.

6-21. TESTING THE SCRAP STRIP Run the strip through the piercing and blanking punch layout A, Fig. 6-19. At station 1 the strip is advanced as close to the. blanking punch as possible. In dimensioning the die, the finger stop should locate the strip 0.010 inch away from the edge of the blanking punch . If the press were tripped, piercing punch A

BACK GAGE

0

A

0

c 0 STATION I

0

D

,(l,

Fig. 6·19. Four piercing and blanking punch layouts traced from Fig. 6-15.

~

8

STATION 2

6-20. TRIAL SCRAP STRIP On another sheet of thin paper, draw the scrap strip as shown at A. For experienced men the two lines shown at B are sufficient for this tryout work.

STATION 3 Fig. 6· 21. Testing the scrap strip for the first layout.

A A

0

8

B Fig. 6·20. Drawing the trial scrap strip.

0 Fig. 6-22. The resulting scrap strip (A) and parts removed (B) in testing the first Iayout.

• OW TO LAY OU T A SCRA P STRIP -ould pierce the first hole. In this paper layout this · ole is drawn on the strip as a circle. At station 2 the =· ip is advanced until the pierced hole is in line with ;i ot B of the blanking punch. If the pres s were now - · pped, blanking punch C wou ld produce a partial bank, -aile the two piercing punches would pierce holes in _.._e s tri p. In our paper strip we duplicate these opera:ions by tracing around the blanking punch to s how ~ i s partial removal of a blank, and around the piercing ? nches, just as the press would do it on an actual 5 ' i p. This can be done free-hand for the time being. At station 3, the strip is advanced again until the ·oles are in line with the pilots. Trippi ng the press ou ld produce a complete blank , and two more pierced ~o es at station 1. Draw the outline of the blanking ; nch and the two holes on the paper strip . With prac~ce th ese operations can be performed very quickly .

6- 22.

EVALUATI~G

81

a long, unsupported cut on one side. An unsupported cut, or unbalanced cut, is one in which cutting occurs along one edge only. The cut is not balanced or supported by a cut at the opposite side. As the punch penetrates the material, side thrust is developed tending to cause the punch to back away with consequent wear of the guide posts and bushings of the die set caused by the increased side pressure. In time , as wear of posts and bushings increased, the blanking punch would be deflected sufficiently to strike the

STATION I

RESULTS

Our scrap strip layout now looks like the one at A, "le the parts removed are shown at B. By analyzing _._. s scrap strip, we see a serious faul t. Tab C, cut ~- station 2, has remained on top of the die block where .: can get under the cutting edge of the blanking punch : ch ip it, or under the piercing punches t o break them. :-: e tab would be produced only at the beginning, and i bly at the end of each strip, but many hundreds of 5' "ps will be run during the life of the die. Rule Num:-e~ 1: Arrange th e first partial blank so an unattached _, ·ece of metal never remain s on top of the di e block.

23 .

TESTI~G

THE

SECO~D

STATION 2

LAYOUT

Ru n a strip through view B of Fig. 6-19. At station : we are unable to bring the strip very close to the : : ank ing punch, for to do so would mean a partial cut -: piercing punch A, which would break it. Use a fin:;:e~ stop to locate the s t rip close to the piercing punch. _,;aw the punch B in position. At station 2, pilot C • x ates the strip, and blanking punch D makes a parcut. Draw the blanking punch outline and the two __ ercing punch circles . At station 3 the bl anking punch :: uces a full blank . Draw the blanking punch and the -.o piercing punch circles.

STATION 3 Fig. 6-23. Testing the scr ap strip for the second layo ut .

A 24.

EVALUATI~G

0 THE STRIP

At A is shown the scrap strip produced by the die ..::. Fi g. 6-23, while at B is illustrated t he partial blank , ·__: bl ank, and pierced slugs removed from it. No slug - eft on top of the die block as in the previous exam:.e. However, it is not good practice to leave a par::- s lug as at C. Because the slug is not gripped securely in the die opening, it can clin g to the face .: th e blanking punch when the press ram goes up th en drop on top of the die block. Another bad ==-a ure of this layout is that the blanking punch makes

c

B

0 Fig. 6· 24. The resu lting scrap stri p ( A} . an d part s remo ved ( B) in tes ti ng the seco nd lay out.

82

HOW TO L AY OUT A SCRA P STRIP

opposite edge of the die block, resulting in nicked cutting edges an-d shortened die life. The effect of side deflection may be observed when we try to cut materia l with scissors that have become somewhat dull. As pressure is applied to cut the material, the blades have a tendency to spread apart or deflect. Rule Num ber 2 is: Avoid cutting long, one-sided portions of a blank unsupported by a balancing cut at the other side. Rule 3 is: Avoid cutting small portions of th e strip not confined in the die block.

6-25. TESTING THE THIRD LAYOUT Thi s layout is opposite to the layout for Fig. 6-21, and th e s ame rules and recommendations apply.

6-26. EVALUATING THE THIRD LAYOUT This scr ap strip is produced by the die in Fig. 6-25. Whi le it does not seem to apply for this particular part, it would be the one to use for some parts with a different contour .

~

J

• Fig. 6-25. Testing the scrap strip for the third layout.

Fi g. 6· 27. Tes ting th e scrap strip for th e fourth layout.

0

0

0

Fig. 6-26. The resulting scra p strip and ports removed in test ing the third layout.

0

Fig. 6- 28. The res ulting sc rap strip and ports removed in te stin g th e fourt h Ioyout.

HO W TO LAY OUT A SCRAP STRIP

6· 27. ~

TESTI~G

83

THE FOURTH LAYOUT

This layout is opposite to the layout for Fig. 6-23, d the same rules and recommendations apply .

6-28. EVALUATI~G THE FOURTH LAYOUT This scrap strip is produced by the die in Fig. _.- 7. It is obvious that none of the four metho ds pro,: ces a trouble free die. These layouts, however, do ;:;. vi de a clue to development of an excellent scrap -tri p. The layout in Fig. 6-21 appe ars promising. · c lination of the part is good for gaging purposes. : he automatic stop should push the strip against ::3e back gage, rather than pull it forward . But we must - d a way to keep tab C attached to the strip, poss:0 y by changing the angle of the blank .

Fig. 6·30. Corrected outline s.

6· 29. AL TERI~G THE LAYOUT Place another sheet of translucent paper over the :ayout in Fig. 6-7 , turned over, and draw two blanks, :eaving a greater distance A between them.

r - ----------- ----·~-----, I

I

I I

Fig. 6· 31. Completed new layout.

0

6·32.

'-----"-.:---- ---- -

--~---'

=ig. 6·29. Tracing a new layout allo wing for a greater space at A.

5·30. CORRECTI~G OUTLI~ES Once again, this layout is fastened to the drafting ·able and, using the protractor, we go over the out. es, straightening them accurately.

6· 31.

~EW

LAYOUT

After tracing the third blank we have a new layout -ri th the part shown with a smaller angle to the hor·zontal than we had in Fig. 6-15. From this we make another piercing and blanking punch layout and run the - ip through it.

TESTI~G

THE

~EW

LAYOUT

At station 1, the strip is brought close to the blanking punch to get the maxium "bite," and the first circle is drawn for piercing punch A. The altered angle creates a scrap bridge to hold the previously loose tab to the strip. Vary this angle until scrap bridge B is same as the scrap bridge between blanks C. Cutting forces are fairly well-balanced . There is little tendency for the blanking punch to deflect with this arrangement. At station 3 a full blank is cut from the strip. Note that the toe of the automatic stop 0 is placed to stop the strip for the first blanking cut at station 2, and it also stops the strip for all succeeding cuts.

6-33. COMPLETED SCRAP STRIP LAYOUT This is how our completed scrap strip appears, along with the partial blank, full blank , and pierced slugs which were removed from it. Die design for this part can now be safely started with full knowledge that a good tool will result.

84

HOW TO LAY OUT A SCRAP STRIP BACK GAGE

STATION I

s-H--

difference . For dies having three or more stations, it is wise to show the outline of the part at every station in either phantom or dotted lines. At station 1 the strip is advanced close to the edge of the center part, and a circle is drawn representing the piercing punch A. At station 2 the strip is advanced until the pilot B loc ates in the previously pierced hole. This should bring the end of the strip 0.010 inch away from blanking punch C. Round-nosed punches Dindent three welding projections in the strip. At station 3 the first partial blank is removed from the strip. Note automatic stop toe E which stops the end of the strip. At station 4, automatic stop toe E stops the strip in the hole of the first partial blank and at the same time the first full blank is produced at station 3, welding projections are applied at station 2, and a hole is pierced at station 1.

STATION 2

STATION I

STATION 3 Fig. 6-32. Testing the new scrap strip layout

0

STATION 3

0 Fig. 6·34. Typical thr ee station layout for a business machine por t. Fig. 6·33. The re sul t in g scrap stri p end ports removed in testing the ne w Icyout .

6-34. THREE-STATION LAYOUTS Introduction of another station between the first piercing station and the blanking station does not alter any of the rules, Here is a 3-station die layout for a typical business-machine part. There is one

6-35. SCRAP STRIP FOR THREE-STATION DIE Here is the scrap strip for the die in Fig. 6-34, as well as the parts removed from it.


85

6·37. SCRAP STRIP FOR FIVE-STATION DIE At A is shown the complete scrap s'trip for this die, while · at B the partial blank, finished blank and pierced slug are shown.

0 SCRAP STRIP ALLOWANCES It is important that correct bridge allowances be applie.d between blanks and between blanks and edge s of the strip. Excessive allowance is wasteful of material. Insufficient allowance results in a weak scrap strip subject to possible breakage with consequent slowdowns on the press line. In addition, a weak scrap area around the blank can cause dishing of the part.

0 ~ig.

6-35. Scrap strip and removed ports lor layou t in Fig. 6·34.

6·38. SCRAP STRIP ALLOWANCES-ONE-PASS LAYOUTS 6-36. FIVE-STATION LAYOUT (See page 86)

Peripheries of blanks may be classified under four distinct outline shapes. In the illustration:

This shows the scrap strip for a 5 station die. At station 1, the strip is advanced close to the dotted part A, and a hole is pierced. At station 2, the strip · s lvcated by pilot B, hole Cis pierced, and embossing ;mnch D applies a bead to a portion of the strip. At s ation 3, a marking punch E stamps the strip, emboss. g punch D applies a full bead to the strip at station 1, and at station 1 the strip is pierced. At station 4 the )lanking punch cuts a partial blank, while members a the previous stations perform their functions . At 5 -· e blanking punch cuts a full blank.

1. Curved outlines. For these, dimensions A are given a minimum allowance of 70 per cent of the strip thickness T. 2. Straight edges. Dimensions of B and B' depend upon the length of the bridge, dimensions L and L', res pecti vel y. Where L or L' is less than 2;6 inches, B or B' = 1 T, respectively. Where L or L' is 2;6 to 8 inches, B or B' = 1Y4 T, respectively.

A

c

8

0 Fig. 6-37. Scrap strip and removed ports lor layout in Fig. 6-36.

c

86


STATION I

'

I

-...'

\

''

\ \ \

STATION 3

STATION 4

STATION 5

Fig. 6· 36. Typical scrap strip far a five ·stotion die.


87

Where L or L' is over 8 inches, B or 8' ,_specti vely. 3. Parallel curves. For work with parallel • e same rules apply as for straight edges and: Where L is less than 2Y.1 inch, C = 1 T. Where L is 2Y.1 to 8 inches, C = T. Where L is over 8 inches, C = 1Y.1 T. 4. Adjacent sharp corners. These form j)Oint for fractures and minimum allowance Cimension 0 on the drawing.

= 1Y.1 T,

SCRAP-STRIP AlLOWANCES FOR TWO-PASS LAYOUTS I

curves,

m

a f~cal is 1~ T,

A

Single-rO\v layout in· tende d fo r two passes t hrough die: A= T

1'-o

I

-000

00)

8

Double -row layout of blanks with c urved outl ines: A = 11~ T

3

4

-= • 6-38. Four classifications of blank peripherie s to aid in deter .. -

ing scrap·strip allowan ces lor one-pass layo uts.

C 39. SCRAP STRIP ALLOWAHCES- TWO-PASS LAYOUTS When the strip is to be run through the die twice ...:; order to remove all the blanks from it, more allow· ~ ce must be provided than is required for one-pass 2youts. This illustration lists minimum scrap bridge ;:;.. owances which should be applied under given con.:! ' ons. Note that single-row layouts A are given more ~l owance than is required for double-row layouts B = d C. This is because the wider double-row s trips : not distort as much in cutting the first row and less ;:.: owance is required. Because of this minimum strip :.is tortion, double-row layouts are preferred.

Double-row

layout

of

pa r ts with straight and curved outli nes: A :::: 1 1 i T

Fig. 6·39. Scrap· strip allowances lor two-pass layout s.

MINIMUM SCRAP-STRIP ALLOWANCES I

+c-3fl0) ~ \ . LJUlJ . :

·0001

.

'

ONE-PASS LAYOUT

Strip Wid t h B 0 to 3 in ..... 3 to 6 in .. 6 to 12 in ... . Over 12 in .. . ,

Space .. 1/ 32 . ... 1/16 . .... 3/ 32 . . . .. 1/8

. .

+<

DOUBLE-PASS LAYOUT

Strip Width B Space A 0 to 3 in ........ .. ..... 1/16 in. 3 to 6 in.. . . .. . 3/ 32 in. 6 to 12 in .. .. 1/ 8 in. Over 12 in .... 5/ 32 in.

A

in. in. in. in .

40. MINIMUM ALLOWANCES Fig. 6-40. Minimum scrap·slrip al lowances.

This table lists minimum scrap bridge allowances both one-pass and two-pass layouts . These values =-ply for thin gages (less than 3/ 64 inch) of stock ere use of the previous rules would give such small ~ owances as to be impractical. Select the value for :;?ace A opposite the appropriate strip width .

D

~ 3~A4

.

1. APPLICATION OF ALLOWANCES This illustration shows how allowances are applied :-- two representative parts. The upper blank is laid _. for single-row , one-pass through the die . The lower :.ank is laid out for double-row, two-passes through the =-.:: . Calculated values are listed under each view . ust be realized that these are minimum allowances that the next larger fractional dimension would ally be used.

==·

a -

-

NO. 16 GA.I.0598l

C =.OS99

0 :.07"-8

~1~ NO. 12 GA .I.I0461

A ' .l 307

Fig. 6·4 1. Applicat ion of allowances for two representative parts.


88

6-42. BLANK AREA CALCULATIONS When it is possible to position blanks in two or more ways in the strip, th~ blank area for each method

is found and the one most economical of material is selected for the die. At A is shown a blank laid out for single-row, one-pass positioning, the most frequently used method. The blank area, (the area of the strip which is used for one part) is found by the following formula: Blank area :: A x B Single-row blanks which must pass through the die twice have their blank area determined by the formula:

Blanks per strip ::

2

O.

5

B

+1

For the waste end:

D = S - [0.5 B (A- 1) + X + Y + 2E]

SINGLE -P ASS LAYO UT

i"'---- ---- - - - --- - -- --- --- ---5- -- ----- --- - --- - -- ----- ·- -

1

&/d~ l

~~~ l( --~ - 8 - -

Blank area = A x B

S - [X + Y + 2E]

B+-B;

-B

-;< 8 + - 8

---1

li +-- B-fY~~ ~ D - ~

This formula applies to the blank layout at B and also for double-row blanks shown at C. TWO-PASS LAYOUT

Sl NGLE ROW- ONE PASS

JTIBGl A

l. -- 8 - - -.- Blank Areo'

A' 8

f62f~F=l

/'"E · · -~i. E : X -+-- --------- 8 ----j- ----- ---:----- Y - - · ·-~f<- - · D ·- -~ 1r--

fig . 6-43. Rep resen tative illustrations for determining the number of blanks in a strip.

6-44. BLANKS Illustrated are a flat blank A, and a bent blank B for which scrap strips are to be laid out. The flat blank could be positioned vertically, horizontally, or at an angle in the strip. The bent blank should be positioned angularly to prevent possible fracture in the subsequent bending operation.

f ig. 6- 42. Repre sentative illustrations for calculating blank areas,

6-43 . NUMBER OF BLANKS PER STRIP F or large blanks it is often necessary to determine the number of blanks in each strip to establish the extent of the waste end D. This has an influence on the blank layout , becau se too great a waste end is unecono mical. The number of blanks per strip for a single-pass layout is found by the formula: Blanks

A

0 9.

10

per strip A = S - [X + y + 2E] t 1 B

For the waste end:

D = S - [B (A - 1) + X + Y + 2E] When strips must make two passes through the die, the following formulas determine the number of blanks per strip and the extent of the waste end:

8

fig. 6-44. Flat (A) and bent (B) blanks.

89


6·45. BLANK POSITIONING This shows six ways in which the parts illustrated in Fig. 6-44 can be positioned for blanking. The strip wi dth for each position, as well as the feed or disance from station to station, are noted . Observe the considerable difference in strip area per blank for the di fferent methods of positioning.

0

Strip Ar«J ptr Blank' 28906 Sq. in.

rM--J A

Strip Area per Blonlt' 3315 Sq. in.

.L

EmJ B

L.--..;:::::::...__;==-------l E

Strip Area per Blank' 2.5312. Sq. in.

Strip Area per Blank ' 3.453 Sq in.

r------- 3{ ---- -~

~-~ - ~ /'- >~-- . -~/- _;. . '

.

.

.

1_~~----~--~----~~

c

Strip Area per Blank' 2.953 Sq. in.

Fig. 6·45. Six ways of positioning blanks.

Stop Area per Blonk•2.9452 Sqm.

Section 7

HOW TO DESIGN DIE BLOCKS ening, and grinding. Observe that each section is pr vided with working holes, that is, holes which engage punches to perform cutting operations on the materia: and with screw and dowel holes which fasten e a~ section to the die set.

Four factors will influence design of the die block for any particular die. They are: 1. Part size 2. Part thickness 3. Intricacy of part contour 4. Type of die. Small dies, such as those for producing businessmachine parts, usually have a solid die block. Only for intricate part contours would the die block be be sectioned to facilitate machining. Large die blocks are made in sections for easy machining, hardening, and grinding. In illustrations to follow are shown twentysix methods of applying die blocks to small, medium, and large cutting dies. These methods further explain Step 2 in Section 5, "Fourteen Steps to Design a Die."

7·2. APPLYING THE 01 E BLOCK Here is the best method of applying the die blod: to any small and medium-size die. Machined into e die block are blanking opening C and piercing holes D. Holes E, located at each corner, are tapped cocpletely through and two dowel holes F are reame · completely th rough the block. Section views A-A and B-B show the fasteni :. method. Foursocket capscrews G securelxJwMt he block to the die holder of the die set. Two dowels H pressed into the die set and partly into the die blo c,.; prevent any poss~ble shifting in operation. Four buttoohead socket screws I fasten the stripper plate an · gages to the die block, while two dowels J mainta·accurate positioning. Distance K, usually ~ inc is the grinding allowance, used up when the scre \\"S and dowels are lowered in repeated sharpening of tt.;die face . A small dowel L locates the right-hand end of \-= back gage to the stripper plate. This dowel is rna·= 3/ 16 inch in diameter. The other screws and dowe:s are never less than 5/ 16 inch diameter for any die Dowels J are made a press fit in the stripper and gages but a sliding fit in the die block. With this constr ction the stripper, back gage, and front spacer can · _ removed quickly for sharpening the die face witho _: removing the die block from the die set. Section C-C shows the method of machining _ die hole and the piercing punch holes, Straight la~:. M is 1/ 8 inch. Angular relief N is made accordin g :values given in the table. Hole 0 in the die set i:: 1/8 inch larger than opening P in the die block -provide 1/16 inch clearance per side.

di:

7-1. DIE BLOCK This is an actual photograph of a die block for a large piercing die. Large die blocks such as this one are composed of sections for easier machining, hard-

Courtesy of Bethlehem Steel Co. Fig. 7-1. Die block for a large piercing die.

90

91

HOW TO DESIGN DIE BLOCKS

SECTION

!A

IB-IB

Complete Die Member

L

SECTION

JA. -fA_ SECTION

STRIP THICKNESS

E

(C - (C

ANGULAR REL IEF

o t o 1/ 16

l/ 4°

l/16 to ) / 16

l/2 °

)/16 to 5/16

J/40

o..r 5/16

10

N

Die Block Fig. 7·2. Method of apply ing a die bloc k to a die.

7·4. PROPORTIONS

;.3. AL TERHATE METHOD Because it conserves tool steel, this method of a die block is recommended when material ~- rtag es exist. Tool steel die block A, made one· : : ' f the normal thickness, has a machine steel spacer 3 un der it. Two long socket .capscrews C fasten the ::e block to the die set, while two dowels D accurately : ate it. Socket button-head screws E fasten the ~ ' pper plate to the die block, while dowels F and G ~= applied as in Fig. 7-2. Section view C-C shows -- e method of machining the die hole and piercing . ...::ch hole. Straight land H is made 1/8 inch . Angular - · ief I follows the values given in the table in Fig . - -_. Slug clearance hole J, 1/ 8 inch larger than K, ~ carried through both the die set and spacer B. ~?ly ing

The minimum distance A from die hole to the outside edge of the die block is normally 1-l/8 the thickness of the die block , B, but this would be increased to Ph times die block thickness for larger dies, or where sharp corners are present in the die hole contour. For very large dies and thick material strip, dimension A might well be made twice the thickness of the die block. The table gives recommended die block heights for various strip thicknesses .

7-5. FOOLPROOFIHG Dies with symmetrical openings can be assembled incorrectly after repair. This occurrence can result in nicked cuttin g edges because of slight mismatching of punch and die members. Prevent this by "foolproofing" the die block. In dimensioning, place one of the dowels a different dista-nce from its nearest screw hole than the other.

92

HOW TO DESIGN DIE BLOCK

SECTION

lB - JB

0 SECTION

JA.-JA

SECT ION

Fig. 7·3. Alternate method of applying a die block to a die.

A

4-4

v---I I

DIE BLOCK HE IGHT

0 to 1/ 16

15/16

1/ 16 to l / 8

1 1/8

1/8 to J/ 16

l )/8

J / 16 to l / 4

1 5/8

over l / 4

l 7/8

8

Fig. 7·4. Relationship of die bloc k height to strip thickness.

~

I I

I

I

I

I

I ST!llP THICKNESS

~

I

~.........----dJ

Fig. 7·5. Mismatching of fastener ho les coiled "foolproofing."

OW TO DESIGN DIE BLOCKS

93

7-6. BLANK EN LARGEMENT When close part toleranc es are present, you should ·- ow how much the blank or hole size will increase die sharpening past the straight land. This table -- sts the amo unt of growth for each 0. 005 inch removed :. m the face of the die block when y.; degree angular :elief is applied. For Y2 degree relief, multiply the .-alues given by 2. For % degree relief, multiply by 3, ~ d for a 1 degree relief, multiply by 4. Of course, -· ere will be no increase in part size for the first 1/ 8 ~ch removed from the face of the die block since this •- a straight land.

Removed !'rom r aoe of d1e 1n sharpening 0. 005 0. 0 I 0 0.015 0,020 0 02 5 0.030 o. 035 o. 040 o. 045 0.050

II Blank opening

A w111

lnorease by thls amount

The die block can then be specified on the drawing by part number, reducing time required for dimensioning. This table shows the most comonly used sizes for small dies.

A

B

c

D

E

p

)

) 1/ 2

5/8

1 )/4

2 1/ 4

15 / 16

# I ( . 272) Dr1ll, 5/16 - 24 Tap Tnru

3

5

5/8

1 J /4

3 ) /4

15/I6

# I ( . 272 I Dr1ll, 5/ 16-24 •,•,.p Thru

4

4

5/8

2 )/4

2 ) /4

15/16

# I ( . 2721 Dr1ll, 5/16- 24 Tap Thru

4

5

5/8

2 )/4

) 3/4-

15/16

#I ( .2721 Dr111, 5/16-24 Tap Thru

4

6

5/8

2 )/4

4 )/4

15/16

#Q ( -3321 Drill, 3/8 - 24 Tap Thru

5

5

)/4

J 1/2

) 1/2

15 / 16

1/Q. ( ,))2) Drill,

5

6

15/16

1/Q. ( . ))21 Dr1ll,

- - - - - • - - • - • - 0, OUUU4)

-

-

-

-

• -

-

-

-

-

-

•

4 1/2

J 1/2

3/8-24 Tap Thru )/8 - 24 Tap Thru

Fig. 7-7. Tabulation of suggested standard die block sizes.

0. 00008 7 U.OOOIJO 0.000174 0 000218 0 . 000261 o. 000305 0 000348 o. 000392 O.OOQ436 o.oss - - - - - - - - - - ~ - 0.000479 0.060 - - - - - - - - - - - - 0.000523 0.065 - • - - • • - - - - - • O.U00566 0,070 - - - - - - - - - - - - 0.000610 0.075 - - - - - - - - - - - - 0 . 000~54 o. 080 - - - - - - - - - - - - o. 000697 0 ,08 5 - - - - - - - - - - - - 0.000741 o. 090 - - - - - - - - - - - - o. 000784 0. 09 5 - - - - - - - - - - - - 0,000828 0,100 - - - - - - - - - - - - O. OOOH72 0.105 - - - - - - - - - - - - 0. 000915 0.110---- - - - - _.- -- 0. 000959 0.115- - - - - - - - - - -- 0,001002 0.120- - - - - - - - - - - • 0 . 001046 0.125 - - - - - - - - - - - - 0.00 1090 0

-

3/4

G

0

0

A

= . 7-6.

Table for determin ing hole size when die is sharpened post ·-e straight lan d.

4 4

c

D

E

p

G

H

7

3/4

2 1/2

5 1/2

2 3/4

#0. ( . 3321 Dr1ll, 3/3 - 24 Tap Thru

1 1/8

8

3/4

2 1/2

6 1/2

3 1/ 4

#Q ( .)32 1 Dr 1l1,

1 1/8

B

J/8 - 24 Tap Thru

-7. STANDARDI ZING Where large quantities of dies are built, time and :xpense can be saved by standardizing on die block - ·zes . These standard blocks can be machined during - ow periods, or by apprentices, and stocked ready for =:.::ti sh -machining when required. An inexpensive drill :g will assure interchangeability of screw holes.

5

8

3/4

J 1i 2

6 1/2

3 1/4

#Q ( . )321 Dr 111, J/3 - 24 Tap Thru

l 1/8

5

10

J/4

3 l/2

8 l/2

4 l/4

#Q ( . ))2 1 Dr1ll , )/8 - 24 Tap Thru

l l/8

6

8

J/4

4 l/2

6 1/2

J 1/4

#Q ( . )321 Dr1ll , J/8- 24 Tap Thru

l l/8

6

10

J/4

4 1/2

8 1/ 2

4 l/4

#Q ( . ))21 Dr1ll, )/8- 24 Tap Thru

1 1/8

7

11

)/4

5 l /2

9 l /2

4 3/4

#Q ( . ))2 1 Dr111, J/8 - 24 Tap Thru

1 l/8

Fig. 7-8. Tabulation of suggested standard medium-size die block sizes.

94


7-10. WEDGE LOCK A tapered wedge, held down by socket capscrews, is often used to clamp split die blocks set into the die set. Knockout pins can be inserted through the holes A for pressing out the wedge.

7-11. DIE BUSHINGS

SECT IO N

.fA - !A

Fig. 7·9. Die block is split for easier machining.

Hardened die bushings, held in machine-steel retainers , are commonly used in large dies where piercing occurs. They conserve tool steel and are easily replaced should edges become chipped or worn. The straight press-fit bushing at A is the type most commonly used. The bushing is made a slip fit for approximately 1/ 8 inch at its lower end. This assures correct alignment while pressing in, an important feature for accurate center-to-center distance between holes. The inside of the bushinghole is ground straight for 1/8 inch. The remainder is given angular relief for proper slug disposal. With spring strippers, the top of the bushing is made flush with the face of its retainer, as shown at B. For heavy material strip, the flanged type C is used to provide greater area against the die set. It is also used when upward pressure would tend to work the bushing upward. Shown at D, a bushing with an irregular hole is kept from turning by a flat ground in the shoulder. This bears against one edge of a slot machined in the retainer. Where space is limited, die bushings can be kept from turning by a key bearin g against a flat ground in the shoulder, as shown at E.

7-12. SHEAR

SECTION

JA-fA

Fig. 7·10 . Sp lit di e block held in place by a tapered wedge.

7-8. MEDIUM-SIZE DIE BLOCKS Tabula ted are the most comonly used sizes of standard die blocks for medium-size die. Tapped holes are us ually ational Fine Thread because they resist loosenin g under vibration better than the Coarse Thread Series.

For large blanks, shear is applied to the face of the die to reduce shock on the press, the force required, and blanking noise. Shear, properly applied , reduces the blanking force by 25 per cent for metals thicker than Y
7·13. ALTERNATE METHOD 7-9. SPLIT DIE BLOCKS When the die block is split for easier machining of the die opening, it is "set in to" the die set. This view shows a split block, pressed into a recess machined in the die holder.

This is a better method of providing angular she ar. The material, securely gripped at the corners betwee the punch and die members, is gradually cut towards the center. Shear is usually applied when blanks are larger than 5 inches by 5 inches, and over 1/16 inc thick.

95


B

A

c

D

E

Fig. 7·11. Several versions of hardened die bushings used for piercing.

96


(

.....

----

--

---

'I

I

I

I

I

I

I

I \

'-

---

~

""'

I

I I

I I

I

I

I

I

-

F i g. 7·1 2. Die block configura ti on for employing shear in producing Iorge blanks .

Fi g. 7·13. Alternat e die block configuration for employing shear in producing large blanks.

7-14. PROVIDING FOR SHEAR IN ROUND DIE BLOCKS

bar than for the previous example. At C a ] essop Rolled Composite which can be purchased in long bars and cut into required lengths is shown . It can be forged to irregular contours without the tool stee l member A breaking away from the soft machine-steel base B. At D the Richard Brothers Composite is shown. It is available only in straight lengths. At E an Ajax Composite section is shown, while at F is illustrated the Allegheny Ludlum Composite section. At G a Superior Composite section is shown. H shows the O.K . Composite section manufactured by the Ohio Knife Company. It can be furnished ready for final machinin g or in bars up to 125 inches long, hardened, groun d, strai ghtened, and ready for use . Thes e composites all have a tool steel cuttin g member electrically welded to a machine steel base which prevents excessive distortion in hardening and provides a soft flan ge for easy machin ing for screws and dowels.

Round die blocks may be given a shearing action by scal lo ping the face in a series of waves around the periphery . Here again, shear depth should not exceed 2/ 3 the thickness of the stock.

7-15. DIE SECTIONS Large die blocks are ma de of section al components, screwed and doweled to the die holder of the die set, with the secti ons butting against each other. A number of types of these composite die sections are available. At A, the section is machined fro m a rectan gular bar of tool steel. This me thod i s obviously wasteful of material and labor. At B is illustrated Penninsular Rolled Stock, avai lable from the Penninsular Steel Company. Its original shape is denoted by phantom lines . Far less machining is required to finish the


97

B

A

c

0

E

F

G

H

Fig. 7-14. Scalloped round die block for empl oyi ng shear.

7-16. PROPORTIONS This table gives recommended proportions of composite die sections. Lengths of straight sections sually do not exceed 12 inches. Curved sections are ordinarily not made longer than 8 inches .

Fig. 7-15. Various types of commercially availab le plain and compos ite die sections.

7-17. CONSTRUCTION Various arrangements of composite sections can be -upplied by the manufacturers, It is obvious that almost any large blanking die can be fabricated from com?osite sections, no matter how intricate the par: ontour. The following lists the names of the various -ections: A. Straight B. Ribbed C. Double D. Face contoured E. Contoured and ribbed F. Forged G. Forged and ribbed H. Circular.

7-18. COMPOSITE LAYOUTS After a large die has been designed , a composite layout is made on heavy paper or cardboard, exactly to scale. No dimensions are used. However, detail numbers, the type of tool steel, and the number of parts required are specified Curved members are forged to this layout, with stock allowed for machining. Note that joint lines for the tool steel faces are staggered or offset and that they never should be located opposite each other. Only the tool steel members of the composites bear against each other at the end to reduce fitting time.

98


PROPORTIONS Qf COMPOSITE

STRIP THICKNESS

A

0 to 3/64

1

3/ 64 to 3/32

1

3/32 t o 9/64

1 1/2

9/64 to 7/32

l

7/32 to 5/16

B

c

2

1

3 min.

2 1/2

1

3 min.

3

1

J min.

J 1/2

1 1/4

3 1/2 min .

*

4 min.

*

D

USE RIBS

1/ 4

J/4 2

lA I

4

r~

SECTION§

~

_l

LWff~ c

~o~-r

l

1/4

4 1/2

1 1/4

4 1/2 min.

*

5

1 1/4

5 min.

*

5 1/2

1 1/4

5 1/2 min.

*

6

1 1/4

6 min.

*

6 1/2

1 1/2

6 1/2 min ,

*

7

1 1/2

7 min.

*

7 1/2

l 1/2

7 1/2 min.

*

8

1 l/2

8 min,

*

8 l/2

1 l /2

8 l/2 min.

*

9

1 1/2

9 min,

*

9 1/2

1 l/2

9 1/2 min,

*

10

1 1/2

10 min,

*

Fig. 7-16. Tabl e of recommended proportions of composite die sect ions.

c

A

E

D

G

F

H

Fig. 7-17. Various configurations of commercially available composite sections.

7-19 . SUPERIOR COMPOSITES Superior Composites, shown at G in Fig. 7-15. are also used extensively for large solid die blocks . Here , a solid tool-steel ring A is torch cut to the shape shown. A hole of the same outside contour is torch cut in the machine-steel base B to receive the tool steel member. The tool steel ring is then welded in position. The machine steel base, which confines the tool steel ring around its periphery, prevents excessive distortion in hardening, and also provides a soft flange for applying screws and dowels which fasten the die block to the die set.

99


_ ___

_....,........._ _..,,.,.. / @ Q!:!I§; 2 REQ'D

® O.H.TS.

1

2 REQ D

PURCHASE FROM : ALLEGHENY LUDLUM STEEL CORP.

Fig. 7·18 . Typi cal composite layout for a large die.

SECTIONING DIE BLOCKS

t

!A

In Fi gs . 7-9 , 7-10, and 7-15, th e subject of sectioning die blocks fo r ease in hardening and grinding was introduced , and it may be well to enter into a more precise understanding of it at this time. For some die hole shapes, sectioning th e die block provides the following distinct advantages: 1. 2. 3. 4.

Difficult machining is avoided Less distortion occurs in hardening Any distortion can be corrected by grinding Inserts can be replaced more quickly in case of breakage.

7·20. FASTENING DIE STEELS

8

SECTION

fA -fA..

:: - - 7-19. One comme rc ia lly available composite as used in a large die block.

s;:~ l i d

Illustrated are two ways of fastening tool steel bars for blanking parts of square or rectangular shape . At A, the bars are set on top of the die set and clamping members C hold the longer side components D from spreading under cutting thrust. The short members are always used as clamps because the greatest amount of side pressure occurs against the longer sides . At B is shown a rectangular sectional die for long runs. It is composed of four bars E arranged as shown. This provides for setting the bars to the exact opening required and it obviates the necessity of accurate


100

@

@ E

@

@

©

@

@

E @

8

@

@ @

@

@

@ @ Fig. 7·'XJ. Methods of fastening die steels.

A-WRONG

B-RIGHT

Fig. 7-23. Correct and incorrect ways of applying break lines in sectioned die blocks.

Fig. 7·21. Die bloc!< sectioned for piercing two rows of rectangular slots.

A

Fig. 7-24. Use of inserts in providing for frail projections.

@@

©@

machining of the members. The assembly is set into the die holder of the die set as in Fig. 7·9.

7-21. SECTIONS FOR SLOTS

B

@@

©©

c

@@

@@

Fig. 7-22. Various sectioned die blocks with center inserts for punching different ar rays of square and rectangular holes.

Die blocks for piercing rows of square or rectan· gular slots are often sectioned. In this example, slots are machined in members A, and member B is a spacer of paper width. The entire assembly is set into a recess in the die set to prevent deflection under cuttin g pressure.

7-22. CENTER INSERTS This shows various groupings of square and redan· gular holes which can be punched with square sectional dies . The die block shown at A consists of four too: steel members C and the center insert D, both hardened and ground. Construction of die blocks B and C is similar. Each would be retained in a pocket milled in the die holder of the die set.


101

1. The insert may consist of a single member. At

7-23. APPL YINC BREAK LINES

A the center plug D of a lamination die is retained in ring C. Slot openings and a center hole have been

The first rule in sectioning die blocks having openings with curved outlines is: Never apply the break i ne tangent to an arc as shown at A because sharp projections C would be weak and subject to breakage. Break lines should cross the centers of radii as at B.

machined in the plug D prior to hardening, grinding, and assembly within ring C. At B is shown a die block for punching two semi-circular openings in a blank. Fitted insert E is provided with a shoulder at the bottom to prevent it from pulling out. 2. The. insert may consist of two members. At A two ground segments are retained in a ring. The die blanks a small ratchet wheel and sectioning simplifies machining of the center opening, At B, a die block for electrical contacts is split in two segments for grinding the opposed halves which define the die opening. A ring keeps the segments from deflecting under cutting pressure. 3. The insert may consist of several members because of the shape of the blank opening. At A, four identical sections compose the die block. At B, the shape of the opening is such that a three-section division is best.

7·24. INSERTS Frail projections should be designed as inserts for easy machining, heat treating, grinding, and replaceent in case of breakage. The upper die block is composed of two side members A and insert B with a sl ender, easily broken projection at one end. The ower die block is composed of four corner members C and D and replaceable insert E.

7·25. DIE SEGMENTS When a portion of the blank outline is circular shape, the die block may be bored to size and :nserts applied to define the remainder of the shape. :1 the illustration , tool steel block A is machined :'or screws and dowels and the large center hole is ":Jored. The block is then hardened and subsequently ground to size. Segments B are machined, hardened, g ound, and placed in position. The assembly is dl en fastened to the die set.

7·26. ROUND SECTIONAL DIE BLOCKS A round sectional die block consists of a hardened an d ground tool steel ring employed to retain inserts r segments and prevent their deflection under cutting ressure. Six representative examples are shown:

Fig. 7·25. Use of ins erts in die block when portion of blank is cir· cu Ior in sh ape.

-..Split on flat

B

2 Fig. 7·26. Six rep resen tativ e examples sho wing use of round sectional di e blocks in retaining inserts or segments.

3

Section 8

HOW TO DESIGN BLANKING PUNCHES Blanking punches range from tiny components for producing watch and instrument parts to large, multiunit members for blanking such parts as automobile fenders, doors, and tops. The size of the blank to be produced determines the type of punch to use. Design considerations include: 1. Stability, to, prevent deflection 2. Adequate screws to overcome stripping load 3. Good doweling practice for accurate location 4. Sectioning, if required, for proper heat treatment. In illustrations to follow are shown twenty-two methods of applying blanking punches to small, medium, and large cutting dies. Covered are such considerations as keying the punch in order to keep it from turning, use of inserts for ease and economy of replacement, use of sectioning to facilitate heat-treating and minimize distortion, use of shedders to prevent clinging of blanks to punch faces, and proper proportions of and construction of blanking punches. These methods further explain Step 3 in Section 5, "14 Steps to Design a Die."

B

8-1. SMALL BLANKING PUNCHES This shows the method of applying a blanking punch for small instrument washers. Body diameter A is made considerably larger than blanking diameter B, Radius C provides supporting material to give rigidity and prevent deflection of the punch upon contact with the material strip. Section view A shows the punch, punch plate, and punch holder as they would appear in the lower left-hand section view of the die drawing. Plan view B shows the same components inverted as they would appear in the upper right-hand view of the drawing.

A Fig. 8·1. Method of applying a blanking punch for small washer s.

102

HOW TO DESIGN BLANKING PUNCHES

©

103

© @

ilf--lr

0

0 L ___J@

ig. 8·2. Method of applying a slightly larger blanking punch.

©

Fig. 8·4. Square-machined turning.

punch

body

for

keep ing punch from

8-2. PIERCE OR BLANK PUNCHES Slightly larger blanking punches for producing circular parts are made in much the same manner as piercing punches. Rules for designing piercing punches will be given in the next section of the book.

8·3. KEYING THE PUNCH Small blanking punches having a cutting end of irregular contour can be kept from turning by a roundend key. This key is retained in an end-milled slot machined in the punch plate and bears against a flat ground in the punch head. Common applications of this construction are small blanking punches for producing clock, watch, and instrument gears.

8~.ALTERNATEMETHOD

Fig. 8·3. One method of keying a blanking punch.

Another method of keeping small, irregular blanking punches from turning is to machine the body square or rectangular in shape. The retainer hole is machined to fit the square or rectangular punch body.

104


©

@t"r:.

:.:.---~1

0

I1~11I

I II

0

I I

~====:.b

@

Fig. 8·5. Inserts used in weak areas of small blanking punches.

Fig. 8·7. Wi dely use d blanking punch for producing overage·size blanks.

8-5. INSERTS Weak areas of small blanking punches are bes t applied as inserts for easy and inexpensive replacement of members in case of breakage. When inserts are used, the blanking punch assembly is backed up by a hardened plate.

8-6. PUNCHES FOR LONG BLANKS OR SLOTS The sides of "narrow-and-long" blanking punches are provided with a radius A. This radius provides extra supporting material for stability to prevent deflection of the cutting end upon contact with the material strip .

8·7. FLANGED PUNCHES

Fig. 8·6. Radius A provides extra support in th is "narrow·and·long" pu nch.

This type of blanking punch is the most widely used , because it is employed to produce averagesize blanks. As in Fig. 8-6, flanges are provided for fastening the blanking punch to the punch holder with screws and dowels. Only the cutting end of the blanking punch is hardened ; the flanges are soft for accurate fitting of dowels at assembly. "Fool-proof" the punc h by offsettin g one of the dowels to assure correct reassembly in die maintenance.


105

©

/;:.,_,

©

I,\.)I _,

0

@

=ig. 8-8. Removing portion of flange to provide clearance for other Jie components.

8-8. CLEARING OTHER COMPONENTS When space is limited, a portion of the flange can 3e removed to provide room for other die components. ~or good stability, flange width A should not be smaller ~h an punch height B.

Fig. 8-9. Large blanking punches do not require flanges,

©

@

0

0

© 0

@

0

8-9. LARGE BLANKING PUNCHES Larger blanking punches do not require flanges. :'hey can be fastened to the punch holder with screws and dowels applied from the back. Dowel holes are sbown all the way through the punch, either full size J as a smaller hole to enable pressing out the dowels :::uring die maintenance.

-10. SECTIONING LARGE PUNCHES Still larger blanking punches can be made in sections ·o facilitate heat-treating and minimize distortion. :::: ach section is individually screwed and doweled to ::j_e punch holder of the die set.

Fig. 8-10. Large blanking punches are sectionalized to fac ilitate heat- treating and minimize distortion.

106


@ 0

A

Fig. 8-11. Large circular blanking punch is made in two parts to con ~erve tool steel.

Fig. 8- 13. Use of a spacer (B) to conserve tool steel.

8-11. CUTTING RINGS

© [0)

0

(Ql

0

0

(0 )

@

0

Blanking punches for large circular blanks can be made in two parts to conserve tool steel and simplify heat-treating. Cutting ring A is located by a round boss which is part of spacer B. This spacer, in turn, is fitted into a recess machined in the punch holder of the die set. With this construction, dowels are not necessary for positioning the punch.

0 (Q )

0

(QI

8-12. CUTTING STEELS The construction method illustrated in Fig. 8-11 can also be used for blanks with irregular contours . Spacer A is machined to accommodate hardened toolsteel pads B and C. Long socket screws, threaded into the tool-steel pads, fasten both the pads and the machine-steel spacer to the punch holder. Dowels accurately locate the entire assembly.

8-13. SPACER

Fig. 8-12. Construction method for I orge blanking punches with irregular contours.

Still another method of conserving tool steel in large dies is to make the cutting member A in one piece, but relatively thin, and back it up with a machine steel spacer B. The assembly is fastened to the punch holder as in Fig. 8-12, and dowels locate the blanking punch in much the same manner.

107


8·14. PROPORTIONS Proportions often used for medium-size blanking punches are: Punch lengtl} A is 1-5/ 8 inch ; flange height 8, 5/ 8 inch. However, when the flange in employed to retain a small piercing punch, height 8 should not be less than 1-1/2 times the piercing punch diameter C for stability.

8-15. SHEDDERS Blanks produced from oiled stock tend to cling to the face of the blanking punch . Spring loaded shedder pins, applied to one side of the punch, will break the adhesion and free the blank from the punch face to to prevent "double blanking." Three methods of applying shedder pins are available. At A, the shedder pin for a small blanking punch is made short, headed, and backed up by a spring and socket set screw. Make the pin from drill rod, hardened, and polished . A clearance hole is provided in the punch holder for removal of the assembly for punch sharpening. In another method, the shedder can be made long as at B. Its head bears against the to~ of the blanking punch, and it is similarly backed up by R spring and socket set screw. At C, a Vlier shedder is illustrated. This device is available from the Vlier Engineering Co. A selfcontained assembly, the shedder consists of a threaded housing containing a shouldered shedder pin and back-up spring. The assembly is inserted in a hole tapped through the blanking punch, and is backed up by a socket set screw. Screwdriver s lot D is used to remove it for punch sharpening.

Fig . 8·14. Typical proportions of med ium-size blanking punches.

A

8-16. TO APPLY SHEAR For cutting large openings in blanks, "shear" (machining punch face so that cutting edge will be presented at an angle to the surface of the material to be cut) is applied to the face of the punch to reduce shock on the press, the force required, and blanking noise. Shear, properly applied, reduces by one quarter the force required to blank metals thicker than ~ inch. When thinner stock is blanked, the reduction in force is as large as one third. Shown here is the most common method of shearing with the face of a large punch. Shear depth A is made two thirds the thickness of the material. Radius B removes the sharp corner to avoid a focal point for stock fracture.

8

8-17. ALTERNATE METHOD D

c Fi g. 8·15 . Different ver sio ns of a shedder assembly which prevents cli nging of blank to punch face.

This is a better method of providing angular shear to a punch. The material is securely gripped at the corners between the punch and die members, and is gradually cut toward the center. Shear is usually applied for openings larger than 5 by 5 inches, and over l / 16 inch thick.


108

@

@

Fig. 8· 16. Punch configuration for applying shear in cutting Iarge openings.

Fig. 8·17. An

8-18. PROVIDING FOR SHEAR IN ROUND PUNCHES

A number of types of these composite sections are available to the designer. At A, the section is machined from a rectangular bar of tool steel, the original bar being shown in phantom lines. This method is obviously wasteful of material and labor. At B is illustrated Penninsular Rolled Stock, available from the Penninsular Steel Co. Its original shape is denoted by phantom lines. Far less machining is required to finish the bar. At C, the Richard Brothers Composite is shown. It is available only in straight lengths. The Jessop Rolled Composite is illustrated at D. This can be purchased in long bars and cut to required section lengths. It can be forged to irregular contours without the tool steel member A breaking away from the soft machine steel base B. At E is illustrated the Allegheny Ludlum Composite Section, while at F the Ajax Composite is shown . The Superior Composite Section appears at G, while at H is shown the O.K. Composite Section manufactured by the Ohio Knife Company. These c omposites all have tool steel cutting members electrically welded to machine steel bases. The soft base prevents excessive distortion in hardening, and it provides a soft flange for easy and accurate machining for screws and dowels.

Round punches can provide a shearing action by scalloping the face of the punch in a series of waves around the periphery. A hole is first drilled through the center to provide relief for the cutting tool which appiies the scalloping. Here again, shear depth should not exceed two-thirds the thickness of the stock.

8-19. SUPERIOR COMPOSITE PUNCHES Superior Composite Blanking Punches, available from the Superior Steel Co., are used extensively for large blank s . A tool steel ring A is torch-cut to the shape required. Machine steel base B, torch-cut to fit within the opening in the tool steel ring, is welded in position. The soft steel base supports the tool steel ring around its inner periphery to prevent excessive distortion in hardening. It also provides a soft inner flange for applying screws and dowels which fasten the blanking punch to the die set.

8-20. PUNCH SECTIONS Large blanking punches are made of sectional components, screwed and doweled to the punch holder of the die set, with sections butting against each other.

alternate punch configuration for applying she ar.


109

8

~~~~

0

~ ~ 0

SECT I 0 N

.JA.-J.A.

r-.!A

A Fig. 8-19. Commercially available composite punc h for large blanks.

B

Fi g. 8-1 8. Scallop ing provides means of applying shear in cutt ing ound holes.

8-21. CONSTRUCTION Various arrangements of composite sections are s hown. It is obvious from the flexibility with which members can be fabricated that almost any large blankin g punch can be built from composite sections no matter how intricate the part contour. Layouts for composite blanking punch sections are drawn at the same time as die sections. This was illustrated in Fig. 7-18 of Section 7, "How to Design Die Blocks." Referring to the illustration, the following list gives the names of the various sections: A. Straight B. Ribbed C. Double D. Face contoured E . Contoured and -ribbed F. Forged G. Forged and ribbed H. Outside flange I. Inside flange.

8·22. PROPORTIONS These are the recommended proportions of composite blanking punch sections. Lengths of straight sections usually do not exceed 12 inches. Curved sections are ordinarily not made longer than 8 inches.

Fig. 8-20 . Vari ous commercial ly available to th e designer.

available

composite

sec ti on s


110

c

8

A

G

H

Fig. 8·21. Various arrangements of composite sections.

PROPORTIONS OF COMPOSITE PUNCH SECTIONS

STRIP THICKNESS

A

0 to 3/64

1

3/64 to 3/32

1 1/4

3/32 t o 9/64

1 1/2

9/64 to 7/32

1 3/4

7/32 to 5/16

2

LID-l

rc~la

_j_

~A~-

USE

B

c

2

1

3 min.

2 1/2

1

3 min.

3

1

J min,

3 1/2

1 1/4

3 1/2 min,

4

1 1/4

4 min.

4 1/2

1 1/4

4 1/2 min,

5

1 1/4

5 min.

5 1/2

1 1/4

5 1/2 min.

6

1 1/4

6 min,

6 1/2

1 1/2

6 1/2 min.

7

1 1/2

7 min.

7 1/2

1 1/2

7 1/2 min.

8

1 1/2

8 min.

8 1/2

1 1/2

8 1/2 mln,

9

1 1/2

9 min,

* * * * * * * * * * * *

9 1/2

1 1/2

9 1/2 min.

*

10

1 1/2

10 min,

*

D

Fig. 8-22. Table of recommended proportions of composite blanking punch sections.

RIBS

Section 9 I

HOW TO DESIGN PIERCING PUNCHES Piercing punches are usually the weakest link in any die design. Therefore, the followin g factors must always be taken into consideration: 1. Make the punches strong enough so that repeated sh ock in operation will not cause fracture 2. Slender punches must be sufficiently guided and supported to insure alignment between punch and die members and to prevent buckling 3. Make provision for easy removal an d replacement of punches in the event of breakage. Illustrated are twenty-nine methods of designing an d applying piercing punches to aid the desi gner in s electing the best type for the particular job. This list covers all frequently used perforators.

for good alignment while pressin g. Shoulder C is usually made 1/ 8 inch larger in diameter than A. Shoulder height D is 1/ 8 to 3/ 16 inch, depending on size. Piercing diameter E is always on the high side of tolerance. For example: If the hole is dimensioned 0.501 d'1ameter on the part print, t he punch diameter . 0 500 would be made 0.501 inch. The blending radius which connects diameters B and E should be as large as possible· and the surface polished smooth because ridges would present foc al points for fracture .

Probably the most commonly used type, shoulder punches are made from a good grade of tool steel, hardened, and ground all over. They are readily available from a number of suppliers. Diameter A is a press fit in the punch plate. Diameer B, which extends at least 1/ 8 inch , is a slip fit

9-2. GUIDING IN THE STRIPPER In first-class dies , small punches under 3/ 16 inch in diameter are usually guided in hardened bushings pressed into the stripper. Larger punches are often guided, particularly when cutting heavy stock if there is a possibility of punch deflection upon contact with the strip. These guide bushings are hardened, then ground on both inside and outside surfaces . Headless drill bushings can often be used for the same application.

Fig. 9· 1. Commonly used shoulder punc h.

Fig. 9-2. Hardened bushings pre ssed in to the stripp er are used lor guiding sma ll punche s.

9-1. SHOULDER PUNCHES

111

HO W TO DESIGN PIE RCING PUNCHES

112

9-3. BACKING PLATES

9-5. A SET SCREW HOLDS THE PUNCH

When heavy stock is being pierced, the punch head is backed up by a backing plate, pressed into a counterbored hole in the punch holder. This plate distributes the thrust over a wider area, and it prevents the punch head from sinking into the relatively soft material of the die set. Backing plates are made of tool steel, hardened , and ground. The small hole through the die set serves two purposes: 1. To accomodate the pilot on· the counterbore and 2. to allow the backing plate to be pressed out for die repair .

For short-run dies, when low accuracy requirements exist , this inexpensive type of punch may be used. It is made of drill rod , machined to size at the cutti ng end. An angular flat is ground on the punch body for the point of the set screw . However, the set screw has a ten dency to "throw over" the punch by the amount of clearance. Therefore , this construction s hould never be used in first class dies.

Fig. 9-5. Set sc rew is use d to hol d punch in short-run dies. Fig. 9-3. Backing plate di str ibutes thru st over a wide area.

9-6. BRIDGING THE GAP

9-4. SET SCREWS BACK UP THE PUNCH Two socket set screws back up the piercing punch in this application. This method of retaining piercing punches has become widely used in recent years and it should be selected whenever possible. Its main advantage is the ease with which a broken punch can be removed and a new one inserted without the necessity of dismantling any part of the die . When dimensioning, mak e sure that the tap drill for the threaded hole is larger than the punch head.

When the punch is located a greater distance fro::. the punch plate edge than standard set screw len gths. a drill rod spacer is used between the punch and the set screw.

Fig. 9-6. Using a drill rod spacer whe n punch is a gre at di stance from punch plate edge.

9-7. LARGE PUNCHES

Fig . 9-4. Set screws used for backing up a piercin g punch.

Punches over 1-1/4 inch in diameter are relieveC. at the center of the cutting face for ease of sharpening. When cutting heavy stock the annular cuttin g ri n.:o A is often scalloped to relieve the shock on the press.

HOW TO DESIGN PIERCING PUNCHES

Fig. 9-7. Large punches ore rel ieved at center for ease of sharpening.

9-8.

STEPPI~G

SMALL

113

Fig. 9-9. Soft shouldered plug is used to retain small piercing punch in flange of Iorge blanking punch.

PU~CHES

A small punch adjacent to a large one is made shorter by two-thirds of the stock thickness. Some material flow occurs as the large punch penetrates the strip . With both punches the same length, the small one would deflected slightly, resulting in a nicked cutting edge and eventual breakage.

Fig. 9-10. Use of aux il iary die block (A) avoids use of excessively long piercing punches.

9-11. RICHARD BROTHERS Fi g. 9-8. Small punch is made shorter to prevent deflection, nicking and breakage.

PU~CHES

These standardized punches are held in their retainers, and also kept from turning, by spring-backed steel balls. These bear against spherical seats machined in the punches. A simple tool pushes up the ball, depressing the spring, for removal of the punch for sharpening or replacement.

9-9. SOFT PLUGS When a small piercing punch is retained in the fl ange of a hardened blanking punch, a soft shouldered plug is pressed into the flange, then bored to retain the piercing punch. Modern practice is to harden only the cutting end of the blanking punch leaving the flange s oft. No bushing is then required.

9-1 0. SPLIT-LEVEL

PIERCI~G

To avoid excessively long piercing punches when punching stepped shapes, add an auxilliary die block, as at A. In this manner both punches can be made the same length for maximum strength and ease of cons truction .

Fig. 9-11. Punch !s held in place by spring-backed steel balls.

114

9-12. HOVIS PUNCHES These standardized punches are held in their retainers, and also kept from turning, by special socket head cap screws, the heads of which bear against grooves machined in the punches. The heads of the retaining screws have milled clearance radii so it is only necessary to give them a quarter turn for removal of the punches.

HOW TO DESIGN PIERCING PUNCHE

9-14. CLOSE PERFORATING Tiny peened-head punches are often arranged in great numbers at very close center distances, as when perforating coffee strainers and similar parts. Such multiple units are backed up by one large hardened plate and the punches are guided in holes in the stripper .

Fig. 9-14. Arrangement of tiny peened-head punches for perforati ng strainers. Fig. 9-12. Punch is held in place by a special socketheadcapscrew.

9-13. PEENING THE HEAD It is difficult and expensive to machine shoulders on punches of very small diameter. For this reason , they are made of plain drill rod for their entire length. One end is peened to form a head and this is finished to an 82 degree included angle to fit standard countersunk holes . At assembly, the top of the punch plate is ground s o the peened heads come flush with its surface. These punches should invariably be backed up by a hardened plate and guided in the stripper. When properly supported in this manner, these punches will pie rce holes with diameters as small as twice the thickness of the s tock.

9-15. STEPPED PERFORATORS Closely spaced peened-head punches, when piercin thicker stock, should be staggered so that not a · punches enter the strip at once. This practice preven s excessive punch breakage due to crowding ofthe met a . Two-thirds of the thickness of the stock is generall_allowed as an offset on punch length.

Fig. 9-15. Punches are staggered to prevent breakage and cro wd i g of metal.

Fig. 9-13. Piercing punch is made by peen ing head on drill rod and grinding to shape and length.

9-16. ALTERNATE METHOD Here is another method of staggering closely spac punches . The center punch enters the material firs . Succeeding punches at either side enter by ste ps . These, again, are made shorter by two-thirds of t e thickness of the stock


115

Fig. 9·16. Another method of staggering c losely spaced punches.

0

9-17. QUILL SUPPORT Very small peened-head punches can be held in quills and guided in hardened bushings pressed into th e stripper. When replacing the punches , simply remove them from their quills and insert new ones. They are backed up by either a hardened plate or socket set screws.

Fig. 9-18. Sometimesthequill itse lf is qu ided by a harde ned bu shing in the stripper.

Fig. 9-19. Two very closely spac ed pe ened-head punches held in a single quill. Fig. 9-17. Support for smal l peened-head punches is provided by a quill in punch plate and hardened bushing in stripper.

9-18. GUIDING THE QUILL Another method of providing lateral support to a small peened-head punch is to guide the quill itself in a hardened bushing in the stripper plate. In this way the punch extends from the quill only a very short distance for maximum stiffness .

9-19. ONE QUILL- TWO PERFORATORS Two or more . closely spaced peened -head punches can be held in a single quill. The quill is kept from turning by a flat machined on one side of its head. This flat bears against one edge of a slot machined in the punch plate. The quill is guided in a hardened bushing in the stripper and the punches are backed up by a backing plate.

9-20. BIT PUNCHES Tiny bit punches, made of top-grade material, are held in a small quill, backed up by a hardened plug. These components are, in turn, held in a larger quill. In this way the punches can be made of expensive material, but the cost compares favorably with larger punches made of lower grade steel.

9-21. DURABLE PUNCHES AND SLEEVES An ingenious method of supporting and guiding slender punches was originated by the Durable Punch and Die Company, which holds a patent. Headed punch A is guided and supported for its entire length in two intermeshing sleeves B and C. The punch extends out of these supporting sleeves only when actually going through the material to be cut. As you may know,

116

Fig. 9-20 . Bit punch enclosed in small quill and in turn enclosed in larger quill and bac ked up may be mode of expensive material.

HOW TO DESIGN PIERCING P UNCHES

Fig. 9·22. Shedd er pin incorporated into pierci ng punch to overcom e tendenc y of slug to follow piercing punch out of die hole.

Fig. 9-21. Me thod of supporting punches with intermeshing sleeves.

a slender needle, passed through a cork, can be driven entirely through a coin by a single hammer blow because of the support given by the surrounding cork. The interme shing action of Durable sleeves supports the punch in much the same manner, allowing the piercing of extremely small holes whose diameters are as little as one-half of the mate rial t hickness. A complete Durable ass embly is shown at D.

Fig. 9·23. Shedder pin made of rubber.

9-23. RUBBER SHEDDER Another method of preventing slugs from pulling up out of the die hole is to insert a rubber bumper in a recessed hole in the punch. The rubber shedder is made with a head to keep it from falling out in operation .

9-22. SHEDDER When piercing s ome thin materials , the slug tends to follow the piercin g punch out of the die hole. This can be a serious proble m in progressive dies. To overco me the trouble, incorporate a shedder pin in the punch. This headed pin is backed up by a sprin g and set screw. Piercing punches provided with shedders are available from a number of suppliers .

9-24. TEMPORARY SOLUTION If slugs are pulling up in the die tryout stage, grind two slots in the cutting face of the punch as shown . This is a temporary measure and a shedder pin should be applied later.


117

.•

Fig. 9·24. Slots ground on end of punch temporar ily serves same pu rpose as shedder pin.

1

I

Fig. 9·26. Retaining key keeps punch from turning.

I I

:1~ I~

I

I

I

I

Fi g. 9·25. Flat on punch head of irregular punch keeps it from turn·

Fig. 9·27. Mating flats of irregular punches keep them from turning.

i g.

9·25. IRREGULAR PUNCHES A good method of keeping an irregular punch from rning is to machine a flat in the punch head. This fla t bears against one edge of a slot machined in the punch plate. A snug fit is required.

end-milled in the punch plate. This method is particularly useful in multiple station progressive dies where space is limited.

9-27. MATING FLATS 9·26. RETAINING KEY Another good method of keeping an irregular punch turning is to machine a flat in the punch head, as before, and insert a small round-end key in a slot ~o m

Where irregular punches are close together , an excellent method of keeping them from turning is to machine flats on both punch heads. These flats bear against each other with a good fit, keeping the punches in alignment.


118

-- ---i

Fig. 9-28. Large punch head may be doweled to kee p punch from tur ni ng.

9-28. DOWELED

PU~CH

HEAD

If an irregular piercing punch is provided with a large head, a small dowel, pressed through both the head and the punch plate will keep the punch in good alignment. This is not considered as good a method as those previously described, but it is used frequently for low and medium production dies .

Fig. 9·29 . A dutchman (small dowel) may be pressed in place on periphery of punch head to keep punch from turning.

9-29.

DUTCHMA~.

A dutchman, that is, a small dowel pressed half in the punch head and half in the punch plate will kee p the punch from turning. As in the previous example, this method should not be used for first-class dies. It is more suitable for temporary dies and dies for low production.

Section 10

HOW TO DESIGN PUNCH PLATES Punch plates hold and support piercing, notching, and cut off punches . They are usually made of machine steel, but can be made of tool steel, left soft, for highgrade dies . Punch plates range from small simple blocks for holding single piercing punches to large, precision-machined plates for holding hundreds of perforators. Important design considerations include: 1. Adequate thickness for proper punch support 2. Good doweling practice to insure accurate location 3. Sufficient screws to overcome stripping load . illustrated are twenty methods of designing punch plates, and applying them to various types of dies . These methods further explain Step 5 in Section 5, "Fourteen Steps to Desi gn a Die" .

10-1. PUNCH PLATES FOR SINGLE PUNCHES A punch plate for holding a single punch is made square, and with sufficient thickness for good punch support. Two socket cap screws, applied at the corners, resist stripping pressure, while dowels at the other two corners provide accurate location. Minimum distance from plate edges to screw centers , A, is 1~ times screw diameter B. 10-2. PUNCH PLATE BUSHINGS Slender punches which are subject to breakage and replacement are retained in hardened bushings pressed into the punch plate. The top of the guide bushing is ground flush with the top of the punch plate after pressing in .

@

0

0

'

0

<;51

Fig. 10-2. Hardened bushing retains slender punch subject to break· age and replacement.

Fig. 10·1. Punch plate for a single pun ch.

119

120

HOW TO DESIGN PUNCH PLATES

10-3. IRREGULAR PUNCHES

IG!

Punch plates that retain irregular piercing punches should have a slot mach~ned in the top surface to the same depth as the punch head. A flat, ground in the punch head, bears against one edge of this slot to prevent turning.

@

0

@] '

0

191

0

ItA iW , .. - 7

0

@

Fig. 10·5. Slot milled in the top of the punch plate retains key for preventing turning.

10-6. STRIPPING FORCE

Fig. 10·3. Slot in the top of punch pi ate provides means of preventing turn ing of punch.

10-4. MULTIPLE IRREGULAR PUNCHES Two, or more, irregular punches which are in line can be kept from turning by a single slot machined in the top of the punch plate, against which flats on the punch head bear. This slot should be made large enough to clear the opposite sides of the punch heads.

When center distances are small, a single punch plate can hold a number of piercing punches. When a large number of punches is retained, the stripping force should be calculated to insure that sufficient screws are used to fasten the punch plate to the die set. The formula: L xT p = 0.00117 where: L = Length of cut, in this case the sum of the perimeters of all piercing punch faces. T = Thickness of stock P = Force in pounds to effect stripping. A discussion on the safe strength of screws is given to accompany Fig. 16-30 in the section on fasteners.

0

IQI

@ /

0

Fig. 10·4. Slot may also be used to keep two or more punches from turning.

©" I

@ I

/

IQI

Fig· 10·6. Single punch plate holds three punches as their center distances are small.

10-5. KEYED PUNCHES Where space is li mi ted a s lot is end-milled in the top of the punch plate to the same depth as the counterbored hole for the punch head. A small round-end key is inserted in this slot. The key engages a flat, machined in the punch head, to keep it from turnin g.

10·7. INDIVIDUAL PUNCH PLATES When piercing punches are some distance from each other, they are preferably held in individual punch plates, as shown. This condition is encountered in large piercing dies.

121


A

0

0

A 0

0

0 5/16 7/16 1/ 2 5/8 11/ 16 3/4 7/8 15/ 16

B

t o 5/16 to 7/ 16 to 1/2 t o 5/8 t o 11/16 t o J/4 t o 7/8 t o 15/16 1 to

1/2 5/8 J/4 7/8 1 1 1/8 1 1/4 1 3/8 1 1/ 2

-l B 1 Fig. 10·9. Table for determining pu nch plate thickness. Fig . 10-7. Indivi dual pu nch plat es are use d when punches ar e some distance from each othei.

10-8. STEPPED PUNCH PLATES When the part to be pierced has two levels, double punch plates avoid long piercing punches. Socket cap screws fasten lower to upper plate. The latter is held to the punch holder from the back. Note the double dowels. It is considered poor 'practice to use extremely long dowels. @

0 4=~ II( )II ~~ ~

0

I

I I

I (()) I

- i

2 2 3 3

3

4

4 4

5 5 5

6 6 6 6 7 7 7

@, 0

B

3

@

I I

A

2

J

4

5 4

5

6 5 6 7 6 7 8 10 7 9

11

Fig. 10·10. Commonly used standard punch plate sizes.

10-11. PURCHAS ED PUNCH PLAT ES

~ i g.

10 -8 . Punch plates are stepped to avoid long piercing punches.

10-9. THICKN ESS Punch plate thickness B should be approximately times diameter A of the piercing punch. With the ·able, the die designer can establish punch plate thickess quickly. 1~

Available from Allied Products Corp., Richard Brothers punch plates can be purchased as standard components to hold the company 's line of piercing punches. Three styles are supplied . At A is shown the round punch plate . It is machined to accomodate a hardened, spring-backed ball which engages a recess machined in the piercing punch. A hardened backing plate, made the same diameter as the punch plate flange, prevents the punch from sinking into the soft material of the punch holder of the die set. The view at B illustrates the more commonly used square punch plate, backed up by a hardened plate of the same size, while at C is shown the end-retaining punch plate, used where space is limited.

10-12. HOVIS PUNCH PLATES Available from Hovis Screwlock Co. , Hovis standard punch plates are used to hold its line of piercing punches. They are retained by special quarter-turn screws that provide quick removal of piercing punches for replacement.

0- 10. STANDARDIZED PUNCH PLAT ES Where large quantities of dies are produced ; time money can be saved by standardizing punch plate -izes and assigning part numbers to them. The most :ommonly used sizes are tabulated. a::~d

10-13. PUNCH PL ATES FOR CU T-OFF PUNCHES There are three commonly used methods of retaining small cut-off punches. At A a large slot, machined in the top s urface of the punch plate, provides clearance

122


for the punch head. Where space limitations exist, a narrower slot is machined as shown at B. End flanges D prevent the cut-off punch from pulling out. Where space is still more limited a recess, slightly larger than the punch head, is end-milled in the top of the punch plate, as shown at C.

@

0

Fig. 10·12. Another type of

commerc ially·avai Iobi e punch pi ate.

10-14. NOTCHING PUNCHES Small notching punches are usually held in thei r punch plate by means of slots machined in the top surface of the plate . Three sides of the punch head bear against the bottom of the machined slot to preven the punch from pulling out.

0 0

@

10-15. COMPOUND DIES Punch plates used in compound dies are made large so they can act as a spacer for inverted die block A. Long socket cap screws, applied from the top of the die set, pass through clearance holes in the punch plate and are threaded into the die bloc k. 10-16. INDIRECT KNOCKOUTS When indirect knockouts are used, the punch pl ate is recessed, as at A, to accommodate the knock ou: plate B. In this case, the recess is shaped in the form of the letter X. 10-17. PUNCH PLATES FOR INVERTED DIES In inverted piercing or shaving dies, the pun6 plate is fastened to the die holder of the die set i stead of being placed in its usual position under e upper punch holder. The illustrated die shaves t" holes. The punches have been inverted to make us e o:: the pressure attachment of the press for more effecti -e stripping. 10-18. HORN DIES Piercing punches used in horn dies are retained i::: a punch plate fastened to the punch holder of the ,. e set. This die pierces a hole in the side of a dr a ~ cup.

Fig. 10·11. Various types of punch plates that ore commercial ly avail· able.

10-19. SIDE-CAM DIES Punch plates for side cam dies usually have e turned boss that engages a counterbored hole in e slide for accurate punch location. With this constructio::: no dowels are required. The die shown at A pierce::: holes in the sides of shells when ·the burr is require::

123


@

0 ~

i~ 'o:',-t::

II

II

11

.

~.l-~,~

~

0

(Q)

Fig. 10·14. Punch plate for notching punches.

@

0

0

0

0

0

(Q) 0

(Q)

0 (Q)

(Q)

0

0

0

Fig. 10-15. Punch plate for compound die.

=· . 10·13. Three commonly used methods of reta ining small cut·off =. nches.

10-20. GUIDED PUNCH PLATES

be inside the shell. The die shown at B pierces in :::te sides of shells when the burr is required to come : side the shell. Construction of the punch plate is Sillilar to A.

For piercing angular holes in shells, the punch plate is made large and guided on the die set guide posts. It retains the spring-backed piercing punch A, which is guided in a hardened bushing B pressed into the punch plate. Hardened buttons limit downward travel of the punch plate.

HOW TO DESIGN PUNCH PLATE

124

Fig. 10·18. Punch plate for horn die •

·~

.

A

I

L__ _~~~~_L~~~

Fig. 10·16. Punch plate for indirect knockouts.

Fig. 10·19. Punch plate for side·cam die.

A

Fig. 10·17. Punch plate lor inverted die.

Fig. 10·20. Typical large punch plote that is quided on die set gui • posts. -

Section 11

HOW TO DESIGN PILOTS Pilots play a vital role in the operation of multi ple-station dies, and many press-line troubles can be traced to their faulty design. In applying pilots the following factors should always be considered: 1. They must be strong enough so repeated shock will not cause fracture. Severe shock is applied to the !)ilot point more often than is realized. Consider that the pilot moves a heavy material strip, almost instantly, into register. Pilot breakage increases cost of the s tamping because hundreds of inaccurate parts may be produced before failures are discovered. Also, there is the danger of costly jams resulting from a broken pilot falling between the cutting edges or forming members of the die. 2. Slender pilots must be sufficiently guided and su pported to prevent bending, which can cause faulty s rip positioning. They should be made of a good grade of tool steel, heat treated to Rockwell C 57 to 60 for aximum toughness and hardness, 3. Provision should be made for quick and easy reoval of the pilots for punch sharpening. Illustrated in this section are numerous methods of ::esigning and applying pilots to aid the designer in sel ecting the best type to use for a particular job.

11 -1. SHOULDER PILOTS The frequently used shoulder pilot A is retained in :; nking punch B by a socket pilot nut C. P ilot holes =.re pierced at the first station . The strip is then loc=·ed by pilots at the second and succeeding stations. ~ e automatic stop is positioned so that the strip is =·op ped with a previously pierced hole 0.010 inch past •· final location. The pilot moves the strip back this = ount to bring it into correct register. This over::avel prevents possible cramping of the strip between

pilot and automatic stop. As shown, the pilot is just contacting one side of the hole in the strip preparatory to bringing it back to true position.

A

Fig. 11· 1. Typical shoulder pilot.

11-2. LOCATING THE STRIP Decent of the upper die has caused the bulletshaped nose of the pilot to move the strip back 0.010 inch and the pilot has entered the strip hole, accurately locating it for the blanking operation. The diameter of pilot shoulder A is an import ant dimension. Too small a diameter, in relation to the hole in the strip, will produce inaccurate parts with varying dimensions between hole and part edges. Too large a dimension results in a tight fit in the strip, with a consequent tendency for the blank to be pulled up out of the die hole. This can be a serious problem in progressive dies . A successful formula is: Diameter A equals the diameter of the pierc125

HOW TO DESIGN PILOT

126

ing punch, less 3 per cent of the strip thickness. For example: If the piercing punch diameter is 0.500, and the strip thickness is #16 gage (0.0625 inch): 0.0625 )( 0.03 0.001875 = Three per cent of strip thickness Subtracting this from the piercing punch diameter: 0.500 - 0.0018 0.4982 =Pilot diameter.

11-4. TO DRAW THE PILOT Six steps are taken to draw the acorn-shaped head of a pilot: 1. The shank and diameter A of the head are drawn with light lines. This is the diameter which actuall · engages the hole in the strip for register . As previous !~· noted, this diameter is 3 per cent of the stock thickness les s than the dlam eter of the punch that pierces the hole in the strip. Thickness B is from ~ to ~ of the stock thickness. 2. The point of the compass is applied at the lower righ t comer and radius R is drawn. 3. The point of the compass is applied at the lowe: left corn er and an opposed radius R is drawn. 4. A circle template is carefully applied and a smaller blending radius is drawn. This radius shoul · be approximately~ of diameter A. It should be darken ec and the line drawn to finished width at this time. 5. Lines of the two large radii are now blackene" and widened to blend with the small radius . 6. The shank is completed and the pilot is now fully drawn.

Fig. 11·2. Shou lder pilot in fully descended position accurately lo cates the strip.

11-3. PILOT PROPORTIONS Further descent of the upper die has now caused the blanking punch to penetrate the material strip to produce a blank. The shoulder pilot is used for holes A from ~ to ~ inch diameter, and it has the following general proportions: Straight engagement length B should be from ~ to % of the stock thickness. For example: For #16 gage (0.0625) this length could be made 1/ 32 inch. Diameter C is made an accurate gage fit. The length of this gage fit engagement D is made approximately three times pilot diameter C. Clearance relief diameter E is usually 1/32 inch larger than body diameter C of the pilot.

- A- A

2

3

4

5

6

Fig. 11·4. Six steps in drawing the head of o pi lot.

11-5. SLOTTED PILOT NUTS lnsteadofbeingdriven by internal hexagon wrenche pilot nuts can be made with a screwdriver slot. Whi:e not considered as good as socket nuts, the slottec. nuts do provide a quick way of making these compo;:ents . Dimensions A and B are grinding allowance norm ally ~ inch, and they are consumed as the blan ki;;~ pun ch is sharpened from time to time during the life : the die. Pilots are removed from the punch before sha~ pening. The gage fit (instead of a press fit) and .e pilot nut, allow quick dismantling.

11-6. PILOT NUTS

Fig. 11·3. With shoulder pilot accurately locating the strip, punch descends to blank port.

Pilot nuts represent the fastest and most conve-ien t method of fastening pilots. Their use allows _ pilots to be quickly removed for sharpening wi tho_: the necessity of disassembling other die parts. Stancardized, and stocked in the tool crib, the pilot n ~ effect substantial savings in both design and man- facture of progressive dies, and further savings on :.e press line in making possible quick pilot removal a;j:.

127

HOW TO DESIGN PILOTS

replacement. The most used sizes will vary from shop to shop, depending on the general sizes of stampings to be run. Cold form the double hexagon hol e before final turning of the outside diameter. Make the nuts from drill rod , heat treated; or machine steel, cyanide hardened.

punch for sharpening by simply removing set screw D. The pilot is moved up to compensate for the amount removed from the punch face in sharpening by loosening the small set screw, raising the pilot slightly, and again locking it in place.

Fig. 11 -5. Pi lot nut with screwdr iver slot mav be mad e quickly.

Fig. 11-7. Straight, headed pilot is used when head is backed up by two socket set screws.

11-7. SET SCREWS BACK THE PI LO T

11 -9. LARGE PILOTS

Straight, headed pilots are used when diameter A is from 3/ 16 to 1/ 4 inch. The head is backed up by two socket set screws. Grindin g allowance B is 1/4 inch . Spacer washers are applied under the pilot head each ime the blanking punch is sharpene d to maintai n proper relationship between the end of the pilot and the face of the blanking punch. Gage fit length C is again made approximately three times the pilot diameter.

Pilots over % inch in diameter are held by a long socket cap screw drilled and counterbored into the punch holder of the die set. The pilot is threaded extra distance A to provide take-up for punch sharpening.

11 -8. SMALL PILO TS For pilots under 1/ 8 inch in diameter, shank A is threaded into pilot nut B, and is backed up by a small set screw C. The entire assembly is, in turn, backed up by a large set screw D, threaded into the punch holder of the die set. The assembly is remo ved from the

11-10. PRESS FIT PILOTS For many ye ars press fitted pilots were almost the only type used in press work, but now they are usually specified only for short run jobs and temporary dies . They can work loose and fall between cutting edges or forming members of the die with disastrous results, or fall through the die allowing perhaps hundreds of parts to be run through the die and spoiled because of fault y location.

DIMENSIONS OF PILOT NUTS Nut Size

Sockot Width Across

Body Dio

Top Sizo NC-3

Body lgth.

c

D

E

#4-48 #S-44 #6-40 #8·36 #10-32

1 1 1 1

~ ~

Thd l9fh.

Sockot Depth

Cloer Hole

F

G

Flats

A No.4 No. 5 *No.6 *No. 8 *No. 10

·~

5; 16 3; 8

1; 8 1; 8 5; 32 3; 16 3; 16 ~ 5; 16 3; 8

B 0.187 0.187 0.257 0.280 0.302 0.403 0.498 0.590

5; 16 3; 8 7j 16

~- 28

y,;

5; 16·24 3; 8-24

5; 8 1

Note : Hexaeon "A" must be double, as shown •Most frequently used sizes Fig. 11-6. Suggested dimensions for standardized pilot nuts.

%

0.076 0.082 0.100 0.112 0.142 0.172 0.23 1 0.250

#32(0.116) #30(0.1285) #27(0.144) #18(0.1695) #9 (0.196) #F(0.257) #P (0.323) #W(0.386)

128

HOW TO DESI GN PILOTS

0

c c

B

A

A

8

c

D

E

MAT

1/8

1/ 8

1/ 32

5/32

3/ 32

D.R.

3/ 16

3/16

) / 64

3/ 16

1/8

D.R.

1/ 4

1/4

1/16

9/32

3/16

D.R.

5/ 16

5/16

5/64

3/8

1/4

D.R.

3/8

3/8

3/32

7/ 16

9/32

D.R.

7/16

7/16

7/64

1/ 2

5/16

D.R.

1/ 2

1/2

1/8

9/16

J/8

D. R.

9/16

9/16

9/64

5/8

7/1 6

D.R.

5/8

5/8

5/32

11/ 16

15/32

D. R.

ll/64

J/4

1/2

D.R .

J/ 16

7/8

9/16

D, R.

Fig . 11-8. Backing up a small pilot with 2 set screws.

ll/16 ll / 16 3/4

3/4

B

Fig. 11·9. Holding a larg e pilot in pl ace usi ng a long socket cop scr ew.

Fig. 11·10. Press fitte d pi lot for shor t ru ns.

~!! 16

A

8

c

D

E

MAT

13/16

13/16

1/2

15/16

5/8

T. S.

7/8

7/8

17/32

1

ll/16

T, S.

15/16

15/16

9/16

1 1/8

3/ 4

T.S.

1

1

5/8

1 1/4

13/ 16

T.S.

1 1/16

1 1/ 16

21/3 2

1 5/16

7/ 8

T.S.

1 1/8

1 1/8

11/ 16

1 7/16

15/ 16

T.S.

1 3/16

1 3/16

23/32

1 1/2

1

T. S.

1 1/4

1 1/4

3/4

1 5/8

1 1/16

T. S.

1 5/16

1 5/16

13/16

1 11/ 16

1 1/8

T.S.

1 3/8

1 3/8

27/32

1 3/4

1 3/16

T. S.

1 1/2

1 1/2

15 /16

1 7/8

l 1/4

T. S.

Fi g. 11 · 11. Tabl e of su ggested di mensi ons of press fi t pil ots.


11-11. PROPORTIONS OF PRESS FIT PILOTS Although press-fitted pilots are not employed as much as in the past, they do have a place in the design of low-production dies for running strip stock. In addition they are frequently used as locators in secondary operation dies, engaging previously pierced holes for performing other operations . This table gives dimensions of pilots from 1/8 inch to 1-1/2 inches in diameter.

11-12. IRREGULAR PILOTS Piloting is often done in holes having irregular shape. The pilots must be radially located in a positive manner. In this ·example, the large, oval-shaped pilot is kept from turning by a dowel inserted half in the pilot body and half in the blanking punch. This dowel is made a press fit in the pilot and a gage fit in the punch to provide for easy removal of the pilot for sharpening the punch face.

129

4. Holes in weak area. Piloting in projecting tabs in impractical because they may deflect before the strip is pulled to position. 5. Holes spaced too closely. Piloting in closely spaced holes does not provide an accurate relationship between holes and outside edges of the blank. 6. Blanks without holes. Piloting is done in the scrap area whenever the blank does not contain holes. 7. Projections in hole. Whenever the hole in the blank contains weak projections which could be bent down by the pilot, indirect piloting should be selected.

PILOT IN HOLES PIEIICE. 2 HOtLS !NSCRAP,~WIK

OUT PM.T

Station. 2

Station/

Stiltion 2

INPARTANDZ HOLES IN SCRAP

Station 1

2 Fig. 11·13. Examples of direct piloting ( 1) and indirect piloting (2).

PART CONDITIONS THAT REQUIRE INDIRECT PILOTING

0

0

Fig. 11·12. Fixed oval-shaped pilot.

0

6:~~~~ DIA

3.

11-13. METHODS OF PILOTING There are two methods of piloting in progressive dies: 1. Direct piloting consists of piloting in holes pierce d in that area of the strip which will become the blank. All pilots described so far have been direct pilots which are retained in the blanking punch. All pilots described hereafter in this section will be indi rect pilots. 2. Indirect piloting consists of piercing holes in the scrap area of the strip and locating in these holes at subsequent operations. Direct piloting is the preferred method, but certain blank conditions require indi rect piloting, as will be explained.

0

J2DIA HOLES

2 HOLtS

0

0

0 HOLES TOO SMALL FOR STURDY PILOTS

CLOSE.

TOLE.I\ANCf. ON HOLES

HOLES CLOSE. TO EDGE. WILL DISTORT PIECE.

0

0

HOLES LOCATED IN IIIE.AK PORTiON OF PiECE

HOLES TOO CLOSE. FOt 1\E.LATiONSHIP WITH EDGE

II LANK

LACKS HOLES

PILOT TO FIT OPEN!NCI MfGHT BEND TONGUE.S

Fig. 11·14. Part conditions that require indirect piloting.

11-14. PART CONDITIONS There are seven conditions that require indirect piloting: 1. Close toierance on holes. Pilots can enlarge ho les in pulling a heavy strip to position. 2. Holes too small. Frail pilots can break or deflect in operation. 3. Holes too close to edges of the blank. Distortion can occur in the blank because of enlargement of holes.

11-15. INDIRECT PILOTS Indirect pilots are similar in construction to piercing punches. In this view, the pilot is shown contacting the strip prior to moving it back 0.010 inch into correct register. Body diameter A is made a light press fit in pilot plate B. Diameter C, usually 1/8 inch


130

long, is a sliding fit in the pilot plate for accurate alignment while pressing in. Shoulder diameter D is generally made 1/8 inch larger than body A. Shoulder height E is from l/8 to 3/ 16 inch, depending on pilot size.

supported in a hardened bushing pressed into the stripper plate. The pilot must be a good sliding fit within this bushing, with from 0.0002 to 0.0005 inch maximum clearance specified.

Fig. 11-17. Hardened bushing in stripper provides greater accuracy. Fig. 11-15. Indirect pilot is similar to piercing punch.

11-16. POSITIONING THE STRIP Descent of the upper die to the lowest position causes the pilot to move the strip back 0.010 inch to correct position. The pilot then enters the hole in the die block to accurately position the strip . This die block hole is made the same as for piercing punches , with a 14 degree taper per side. Directly underneath, a clearance hole is applied to the die holder of the die set. In cases of mis-feed , pilots will punch the strip like a piercing punch, and provision must be made for dispos al of slugs. Otherwise , they would pile up and in time the pilot would be broken. Pilot diameter A s hould be a good sliding fit in the pilot hole in the die block , with from 0. 0002 to 0.0005 inch maximum clearance allowed.

11-18. BACKING PLATES Considerably more pressure is requi red for a pilot to pierce a strip than for an equivalent piercing punch . When the possibility is present of repeated mis-feeds , the pilot should be backed up by a hardened plate to prevent its head from sinking into the punch holde r.

Fig. 11 · 18. Pilot backed up with hardened plate when chance of repeated mi s· feeds is present.

11-19. SMALL INDIRECT PILOTS

Fig. 11-16. Indirect pi lot locates the str ip.

1n

full

descended pos ition ac curately

11-17. GUIDING IN THE STRIPPER Where considerable accuracy is required, and when moving a large, heavy strip , the pilot is guided and

Smaller pilots, 3/ 16 to 1/ 4 inch in diameter, are made with a turned head, and are guided in a harden ee bushing in the stripper plate, and backed up by two socket set screws. In every instance the desi gne~ should pay particular attention to grinding allowances . remembering that as punches are sharpened the positions of the pilots will be altered. In this case grinding allowance A is applied to assure that, as the pilots are raised with spacer washers when punch es are sh arpened, the upper socket set screw will no· protrude above the punch holder.


A

- ig. 11·19. Small indirectpilot is guided through stripper by hardened Dushing and is backed up by two set screws.

131

and ground tool steel, support the pilot close to the piloting end.

Fig. 11·21. Method of holding pilot with set screw in temporary dies.

11-20. PEENING THE HEAD Smaller pilots, 1/8 to 3/ 16 inch in diameter can be made of drill rod with a peened head. Such pilots are guided in hardened bushings in the stripper, and are always backed up, either by a hardened plate or with socket set screws. After peening, the head is achined to an 82 degree included angle to fit standard ountersunk holes. At assembly the top of the pilot p ate is ground so that the peened head is flush with 1 s surface.

Fig. 11·22. A small peened-head type pilot held in a qui ll and backed up by a set screw.

=ig. 11·20. Small indirect pilot made of drill rod has a peened head.

11-21. A SET SCREW HOLDS THE PILOT For temporary dies, and where low-accuracy and ow-production requirements exist, pilots can be held ':Jy a socket set screw bearing against a tapered flat achined in the pilot body. These pilots are made of j rill rod, and the bullet-shaped end is machined to suit :.ie hole size. Since the set screw has a tendency to 'throw over" the pilot by the amount of clearance, <1is typeofpilotshould never be used for Class A dies.

11-22. QUILL PILOTS Small pilots, 1/8 inch diameter and smaller, are of til e peened-head type, held in a quill, and backed up · y a socket set screw. These quills, made of hardened

11-23. QUILL ANO BUSHING If the quill is made shorter than shown in Fig. 11-22, the pilot is guided and supported in a hardened bushing pressed into the stripper plate. The entire assembly is backed up eill}er by a hardened plate, or by two set screws. Whenever a hardened plate is used to back up a pilot, a through hole should be drilled in the punch holder for pressing the plate out. When the punches are sharpened, an equal amount of stock may be removed from the backing plate to maintain the relationship between the ends of the pilots and the cutting faces of the punches.

11-24. SPRING-BACKED PILOTS So far, all pilots described have been of the solid variety used for sizes of stock up to and including #16 gage. When piloting in thicker material it is wise to use the spring-backed type of pilot. Pilot A, guided in bushings B and C, is backed up by spring D which is, in turn, backed up by set screw E. The pilot is made a close sliding fit in bushings B and C, normally with from 0.0002 to 0.0005 inch clearance.


132

Fig, 11·23. Pilot similar to the one shown in Fig. 11·22 but with hardened bushi ng in stripper plate and hardened bock up plate.

E

Fi g. 11·25. Position of pilot during a mis·feed.

0

A

8

c Fig. 11·24. Typical spring-backed pilot.

11-25. MI S-FEEDS In the event of a mis-feed the spring-backed pilot retracts harm lessly, as shown. Spring pressure is determined by trial and error. Sufficient pressure must be applied to mov e the strip to correct register at every hit. However, the pressure must not be great enough for the pilot to pierce the strip in the event of a misfee d. Even though a spring-backed pilot is used, the hole in th e die block is made as though for a piercing punch . Whil e the pilot is supposed to retract rather than pierce the stri p, nevertheless the pilot can become frozen in its bushing and pierce instead of re tract. For trouble-free operation , the spring should not be compressed for more than 1/ 3 of its free length, including the initial compression applied when the set screw is inserted .

11-26. SMALL SPRING-BACKED PILOTS Pilots from 3/ 16 to 1/ 4 inch in diameter are made straight and provided wi th a shouldered head. These

Fig. 11·26. Small spring-backed pilot has shouldered head.

also are guided in hardened bushings pressed into the pilot plate and into the stripper plate . A spring an · set screw, inserted in the punch holder, back up the pilot.

11-27. SPRING-BACKED QUILLS Still smaller pilots can be held in quills and backe · up by socket set screws. The quyll is then guided i.r. hardened bushings pressed into the pilot plate an · into the stripper plate. A spring backs up the quill an · it is , in turn , backed up by a large socket set screw. This construction will prevent injury to small pilo and when mis· feeds can occur frequently , this desi should be used.


133

H Fig. ll-27. Small spring-backed pilot-bearing qui ll setup with hard· ened bush ings in pi lot and stripper plates.

Fig. ll-28. Type of pilot used when stock is th ick.

11-28. PILOTING IN HEAVY STRIPS This type of pilot is provided when the stock is un usually thick, or the strip unusually wide and heavy. Pilot A is provided with a thick head into which a hole is drilled and reamed Detent B, backed up by spring C, is inserted in this hole, and its angular face fits in to a groove machined inside of bushing D. Spring E and socket set screw F back up the assembly. The pilot is guided and supported in bushin gs G and H, pressed into the pilot plate and into the stripper plate. The angle on the face of detent B is usually made 40 degrees, but it can be varied to release the pilot under any required pressure .

for Fig. 11· 29, and locating this flat against a key inserted in the pilot plate . Always us.e the round ·end type of key. The fit must be of first-class die quality .

11-29. FLAT ON PILOT HE AD Some indirect pilots are used at intermediate stations of progressive dies for locating the strip . When these ?ilots are engaged in holes other than round , they can be i;ept from turning by grinding a flat on the pilot head. This flat bears against one side of a slot machined in :he pilot plate.

I

I _I

~~ I~ ~

I

11 -30. KEYED PILOTS Where space is limited, the pilot can be kept from . rning by grinding a flat in the same way as described

Fig. 11·29. Triangular-shaped indirect pi lot that is kept from tuming by the flat on the pilot head.

134


Fig. 11·30. Pilot may be keyed with round•end key where space is limited.

Fig. 11·32. Usi ng a dutchman to keep a pilot from turning in temp er· ory dies.

11-31. PINNEO PILOT Another method of keeping an irregular pilot fro;:: turning is to provide a large flanged head on the pi lo· Dowel this flange to the pilot plate.

/- .,_

(@\

I L, Ol \

, _ /

I

Fig. ll -3l.Method of pinn ing on irregu lar pi lot to keep it fr om turning.

11-32. DUTCHMAN When space is limited, a dutchman, pressed half ic the pilot head and half in the pilot plate, will kee p a:: irregular pilot from turning. This method is not cor:· sidered as good as those previously described. It shou be used only for temporary dies where low-produc ti requirements are present.

Section 12

HOW TO DESIGN GAGES Gages must be considered in the desi gn of press tools because these components position the strip longitudinally in its travel through the die . In secondoperation dies , gages locate the previously blanked or formed part for further processing operations. Design considerations include : 1. Material choice . Brown & Sharpe ga ge stock, or an equivalent finished tool steel, is used for gages in first-class dies. Cold-rolled steel should be used only when low-production requirements exist. 2. Adequate thickness . The back ga ge and front spacer must be thick enough to avoid binding of the strip between stripper plate and die block, because of possible camber in the strip. Camber, or curvature, is more pronounced in coiled stock not passed through a s traigh tener. 3. Good doweling practice. Since gages locate the s trip or part, they should always be doweled in position 4. Accuracy of location . Dimensions fro m die hole to locating surfaces of gages are always given decimally on the drawing. S. Accuracy of locating surfaces . The gaging surfaces which actually bear against the strip, or part, should be ground, and so marked on the die drawing. Illustrated in this section are twenty-two methods of applying gages to various types of dies. These methods further explain Step 7 in Section 5, "14 Steps to Design a Die" .

button head screws, passing through the back gage, are threaded into holes tapped in the strip support. At F the components are riveted together, while at G they are welded together. The stripper is relieved 3/ 8 inch, as shown, to help in starting new strips through the die. The relief forms a shelf on which the end of the strip can be dropped, then advanced over the die block surface.

12-l. BACK GAGE AND FRONT SPACER In passing through a two-station pierce and blank die, the strip is positioned against back gage A by the operator. Strip support B helps to align the bottom of the strip with the top surface of the die block to prevent binding. Dimension C, between the back gage and front spacer, is made strip thickness plus 1/ 32 inch when a roll feed is used; strip thickness plus 1/16 to 3/ 16 inch for hand feeding. Thickness 0 of bo th back gage and front spacer is usually made 1/ 8 inch for strip thicknesses up to #16 gage (0.0625 in ch). For heavier strip, dimension D is made strip th ickness plus 1/16 to 1/8 inch. Shown at E, F and G are the three methods of fastening the strip support to the back gage. At E socket

Fig. 12-1. Arrangement of the back gage and front spacer in a twastation pierce and blank die.

135

HOW TO DESIGN GAGE

136

12-2. COMPOUND DIES

12-4. FEEDING THIN STRIPS

In compound dies the back end of the spring stripper A is extended to provide a pad for fastening back gage B. Strip support C completes the assembly. A pin D, pressed into the spring stripper, helps alignment of the strip .

When feeding thin, pliable strips, support A is made long and brought up close to the die block to provide better support and guidance. Three socket button-head screws are provided, but no dowels are required.

Fig. 12· 2. Compound die in which spring stripper (A), back gage (B) and pin (D) help to provide alignment. Fig. 12·4. Support (A) provides extra support for thin, pliable str i s..

12-3. CUT -OFF Dl ES A convenient method of providing a stop for cut-off dies for long parts is to extend the back gage to the left and screw and dowel strip stop A to it as shown . After they have been cut, the blanks slide to the side of the die by means of the angular relief provided in the die block.

Fig. 12·3. Back gage in this cut-off die has been extended to the left to provide mounting for a stop.

12-5. ALTERNATE METHOD This is a better method of supporting and guidi g thin strips and, in fact, may be used for any stri;

0

Fig. 12·5. Another method of supporting and guiding thin st

i ~ s..

137

HOW TO DESIGN GAGES

thickness. The front spacer is extended to the right and an ear on strip support A is fastened under it with a socket button-head screw to provide rigidity. With this method it is not neces.sary to cut a portion of the stripper for starting the strip.

12·6. ROLL FEEDS Strip supports are not required when a roll feed is used. The back gage extends to the right a short distance and the stripper plate is relieved to aid in starting a new strip. Guide length A is made approximately 1~ times the back gage width B.

12·7. STOCK PUSHERS Means are often provided to keep the strip firmly against the back gage during its travel through the die , particularly when a roil feed is used. The simplest method is to apply a stock pusher A, made much like a finger stop. A spring, held by a shoulder screw, applies pressure to register the strip.

12-8. BAR PUSHER An alternative method of applying a stock pusher to a die is to use a flat spring A. This applies pressure through two pins B to pusher bar C to locate the strip firmly against the back gage.

Fig. 12·6. Arrangemen! of back gage and Iron! spacer when roll feed · s used. Fig. 12·8. Ano!her me!hod of applying a slack pusher !o a die.

12-9. ROLLER PUSHER This stock pusher incorporates roller A which is mounted on pi voting arm B by a shoulder screw . Spring C pulls the roller toward the back of the die to position the strip.

12·10. STRIP EQUALIZERS When the strip width tends to vary, a strip equalizer should be used instead of a back gage. This is probably the best type. Arms A and B, pivoting on shoulder screws C, are linked by arm D. Four rollers E guide the strip, acted upon by spring F. Arm B is extended to provide a handle for starting the strip through the die.

12-11. PIN GAGING

END SECT'ON VIEW

ig. 12·7. Me!hod of keeping s!rip firmly agains! back gage by em· oloying slack pusher (A).

Gaging methods for secondary-operation dies usually take the form of nests into which the parts are dropped. Shown here is a die for piercing two holes in squaresheared blanks . When low-production requirements are present, the blank is simply located against three pins . Always position the two in-line locating pins against the longer side of the blank and the single pin against the short side.

138

HOW TO DESIGN GAGE

0

0

Fig. 12·11. Blan k location provided by three dowel pins for lo · productio n secondary requirement s.

Fig. 12-9. Stock pusher that incorporates a roller.

12-12. BEVELED GAGE PINS For higher production requirements, the blank L located in a gage composed of six pins. These are beveled leaving a straight land, equal to the st oc'· thickness, for register. The beveled pins help slide the part to position quickly.

Fig. 12-10. Setup employing a strip equalizer instead of a back gage when the strip width varies.

Fig. 12-12. Beveled gage pins facilitate qu ick positioning for hig ~ production requirements.

139

HOW TO DESIGN GAGES

12-13. TURNED BEVELS Perhaps a better method of applying a bevel to gage pins is to' taper turn the ends of the pins as shown. Thus, even if one pin should loosen and turn , blank positioning would not be affected.

12-15. SPRING PUSHERS When dimensions A and B of the part must be held very accurately, three spring pushers C, confined in spring housings 0 , locate the part against gages E.

Fig. 12· 13. Alternate method of applying bevel to pins. Fig. 12·15. Spring pusher s (C) provide accurate positioning.

12-14. DISAPPEARING PINS If the nature of the operation would cause the punch to strike the locatin g pins, they are made of the disappearing type. Springs, backed up by socket set screws, act against shoulders machined in the locating pins.

Fig. 12-14. Locating pins may be spring-backed if interference is expected.

12·16. LOCATING PADS For high production and long life, the part would be located against locating pads A, held in housings B instead of against pins as in previous examples. These pads are hardened and ground and they are retain ed by socket button-head screws .

Fig. 12-16. Locating pods (A) may be used in lieu of pin s for high production and long life.

140

HOW TO DESIGN GAGES

12-17. PILOT GAGING Use pilots for location when the part contains holes . Pilots provide quick part positioning and are inexpensive. Frequently used sizes are tabulated in Fig. 11-11 of the previous section of the book.

Fig. 12-17. Pilots provide quick port positioning.

12-19. V GAGING Parts with opposed outside radii are located in V gages as shown. Engaging faces of each V are tapered for quick part insertion. A straight land, equal in length to the blank thickness, is left for proper positioning of the part.

Fig. 12-19. Positioning part with V gages.

12-18. RADIUS GAGING Many parts contain internal radii somewhere around their peripheries. Pilots, engaging in these radii, effectively locate the blanks for subsequent operations.

12-20. RELIEVED GAGES Parts with irregular outside contours are located in gages machined to fit the contour, but relieved so that theybearonlyat important points.

Fig. 12-18. Pilots used on outside periphery for positionir.g port.

Fig. 12-20. Gages machined to the outside contour of the part are usee for positioning irregularly shaped pieces.

141

HOW TO DESIGN GAGES

12-21. INTERNAL GAGES

12-22. GAGES FOR SHAVING DIES

Formed or drawn parts are located for further processing by gages machined to fit the inside contours, but relieved so as to bear only at critical points. This die trims the flange of a previously drawn shell.

Gages for shaving dies are made to fit the outside contours of the blank, but relieved so they bear only at required points. Bearing areas are beveled to provide room for the curled chip produced by shaving action. Depth of this relief should be two-thirds of the part thickness. For shaving, die sets with floating adapters should be used, as shown .

Fig. 12·21. Gage machined to fit the inside coutour of formed or drown ports.

Fig. 12·22. Typical gage for shaving die.

Section 13

HOW TO DESIGN FINGER STOPS Finger stops, or primary stops as they are sometimes called, are used in dies with two or more stations . They register the strip for performing operations prior to strip engagement by the automatic stop or roll feed . The number of finger stops used depends upon the number of stations in the die. For hand feeding it is always one less than the total number of stations. For automatic feeding only one finger stop is required. Finger stops are made of cold-rolled steel, cyanide hardened. In the early days of press work, numerous verticallyacting primary stops were used. The hazard of placing fingers between upper and lower die members has caused them to fall in to disrepute . Presently, almost the only finger stops used in modern plants are the horizontal types to be described . Illustrated are fifteen standardized finger stops fully tabulated to aid the designer in selecting the right one for the conditions encountered. Machining data are given for accompanying front spacers. In addition general rules are outlined to help in the correct selection and application of these die components. This furthe r explains Step 8 in Section 5, "Fourteen Steps to Design a Die."

pierced at the first station, and the blank is removed from the strip at the second station. Finger stop A has been advanced to operating position; the strip is pushed against its toe by the operator, and the press is tripped, piercing the two holes. The toe of automatic stop B has been pulled to the right by the automatic stop sprin g.

13-2. WITHDRAWING THE STOP The finger stop has now been pulled back by the operator, allowing the strip to be moved toward the le until it contacts the toe of the automatic stop, "se ting" it. Tripping the press produces a full blank anc two pierced holes. Subsequently, the operator simply keeps the strip firmly against the automatic stop un · all blanks have been removed. Usually, convention~ front and side section views of the die are used show the form of blanking and piercing punches. So. on the die drawing the side view of the finger stop · s projected to the right as a partial section view, A.

13-1. OPERATION Taken togeth er, this illustration and Fig. 13·2 explain the operation of a typical finger stop. As shown in this plan view of a two-station die, two holes are A

Fig. 13·2. Finger stop in pulled back position allows strip to :: moved to the automatic stop.

13-3. CONSTRUCTION Three common methods of making finger stops a:"' illustrated. At A the bottom of the stop is milled ~ provide a slot for limiting stop travel, and to retain e stopinthefrontspacer. The stop at B has an end-mille:: slot machined along its center. A dowel engages ·slot to limit s top travel. Similarly, the stop at C he:= a partial slot cut along its edge to limit travel. Because does not require a dowel, the stop at A is preferre ·

A

Fig. 13·1. Finger stop (A) is in posit ion to stop the strip for the piercing operation.

142

HOW TO DESIGN FINGER STOPS

The designer should always be on the lookout for ways to eliminate unnecessary parts . Also, end-milling of long, narrow slots is slow and therefore expensive.

143

die. In such applications the end of the finger stop is beveled to the angle applied to the strip end.

13-6. INTERFERENCES Always check carefully to make sure that the corner of the finger stop will not be sheared off by the blanking punch in its downward travel. Where interference occurs, bevel the end of the finger stop.

Fig. 13-3. Three common methods of making finger stops.

13-4. MULTIPLE STOPS In multiple station dies designed for hand feeding, finger stops locate the end of the strip for each station ex cept the final automatic stop station. In this die two extruded bosses are applied to the strip at the first station, stop A positioning the strip. Two holes are pierced at the second station, Stop B engaging the end of the strip for locating them. At station 3 the part is bl anked, automatic stop C locating the strip end. When a roll feed is used, only one finger stop is required, applied at the first station . The roll feed advances and positions the strip for all subsequent stations. Pilots perform the final accurate positioning.

Fig. 13-6. End of finger stop is beveled to avoid interference with punch .

13-7. RETURN SPRING A return spring is not ordinarily required on finger stops. However, when the front edge of the material is notched, and a possibility exists that the stop might work inward under vibration and engage the notch to cause a misfeed, a return s pring would be used. A small guide pin, riveted to the finger stop , holds and guides the spring.

Fig. 13·4. Multiple station die employing two finger stops.

13·5. BEVELING THE STOP For some part contours it is necessary to shear the end of the strip at an angle for starting it through the

Fig. 13·7. Finger stop with return spring for avoiding misfeeds on notched strips.

13-8. SPRING STRIPPER

Fi g. 13·5. Finger stop with bevel to conform to pre-sheared strip.

When a spring stripper is used, the slot in the finger stop is inverted. This provides a convenient means of retaining the stop in the front stock guide.

5!36

144

HOW TO DESIGN FINGER STOP

Front spacer width, in turn, is governed by the minimum distance C, of the die block, whi-ch can be used for the particular job. Minimum distance C of the die block depends almost entirely on the contour of the die hole. Secondary considerations are: 1. Extent of straight lands. Where these are lon g the die block is subjected to considerable side pressure during the cutting process . It is often advisable to use a minimum distance C in the thicker ranges regardless of die-hole contour 2. Size of the die hole opening. When openings are large and material strip is thick, it is wise to go to the thicker C ranges regardless of die hole contour. For die holes with smooth, or rounded contours . view 1, minimum distance C is generally 1-1/8 ti mes the thickness B of the die block. When the die hole contains inside corners, view 2, minimum distance C is generally 1¥2 times die block thickness B. View shows severe inside corners in the die hole contouJ, Minimum distance C is then made twice the thicknes s of the die block. These minimum distances are tabulated for recommended die block heights, which i.;: turn are governed by strip thickness A.

Fig. 13·8. Slot in finger stop is inverted when spring stripper is used.

13-9. PROPORTIONS OF DIE BLOCKS Finger stop proportions can only be determined after the width of the front spacer has been established .

rr=-

=;]

I I

I(Q)

I ...._..

C

I

I t(j) 1-...-

t= __ ::!J

A

3

c

•

A

8

STRIP THICKNESS

DIE BLOCK HEIGHT

0 to 1/ 16 1/ 16 to 1/8 l /8 t o 3/ 16 3/16 t o 1/ 4 over 1/4

15/16 1 1/8 1 3/8 1 5/8 1 7/8

MINIMUM DISTANCE - DIE HOLE TO OUTSIDE EDGE

I

2

SMOOTH DIE HOLE CONTOUR

INSIDE CORNERS

( 1 1/8 B)

(1 1/2 B)

1. 0547 1. 2656 1.5469 1.8281 2.1094

3

SHARP INSIDE CORNERS

1.4062 1.6875 2. 0625 2.4375 2.8125

Fig . 13·9 . Recommended minimum C distances for various die hole contours and die block heights (B).

(2 B)

1.875 2.250 2.750 3. 250 ).750


145

®o

----T-r----

@)

o@)

· 11

STRIP THICKNESS 0 to 1/16 1/16 to 1/8 1/8 to )/16 )/16 to l/4 over 1/4

A

A

HAND FEED

POWER FEED

1/16 3)12 1 8 5/)2 )/16

1/32 1/)2 1/32 1/32 1/32

Fig . 13-10. Table of recommen ded A distances for bo th hand and power fee ds.

A

8

STRIP THICKXESS FRONT SPACER THICKNESS 0 to 1/16 l/l6 to 1/8 1/ 8 to J/16 3/ 16 to 1/4 1/ 4 to 5/16

l/8 3/16 1/4 5/16 3/B

Fig. 13-11. Table of recommended fron t spacer thicknesses.

HOW TO DESIGN F INGER STOP

146

13-10. STRIP CLEARANCE Another factor must be known before finger stop proportions can be determined. Distance A between the strip edge and the front spacer must be established because this determines the amount of finger stop travel requi red to stop the strip in a positive manner. Tabulated are recommended distances A for hand feeding using an automa tic stop, and power feeding using a roll feed or hitch feed. Distances A are given for various strip thicknesses.

13-11 . FRONT SPACER THICKNESS Recommended front spacer thicknesses are tabulated. These allow a minimum of 1/ 16 inch clearance between the top of the strip and the underside of the stripper plate to provide for possible curvature in the strip.

curved, it would fall in the second line: Strip Thic kness A - 1/ 16 to 1/ 8. Recommended front spacer width for this condition is 1~ inches, and finger stop No. 2 should be used . The 1~ inch dimension corresponds roughly to line 2 of table 13-9 for smooth die hole contour with a dimension of 1.2656 inches. For l/32 inch thick strip, with sharp inside corners in the die hole, front spacer width, line 1, would be 2 inches and finger s top No . 11 should be used . Of course, sli gh modifications may be necessary for some dies. When in doubt as to correct classification of the die hole contour, use the next greater minimum distance. Only the front spacer width and thickness have been menti oned, but it is understood that the back gage is made the same width and thickness.

13-13. DIMENSIONS 13- 12. PROPORTIONS OF FINGER STOPS Proportions of these fifteen finger stops enable ready selec tion for almost any die design and they assure positive s topping of the strip. In both the forward and return positions the maximum thicknesses of the stops remain confined in the front spacer for strength. This table corresponds, for practical purposes, to the one in Fig. 13-9, and from it the designer can choose the most suitable finger stop for the conditions confronting him. For example, if 3/ 32 inch thick strip is to be run, and the die hole contour is smooth and

A STRIP . HICKNESS 0 to 1/ 16 1/ 16 to 1/ 8 1/8 t o J / 16 J/16 to 1/ 4 over 1/ 4

All dimensions necessary are given for making finge: stops ranging from No. 1 to 15. From this table the design er can apply dimensions quickly, or the fin ge: stop can be specified by number when finger stops have been standardized. Note that: 1. Stops 1 to 5 are used when smooth contours are present in the die hole 2. Stops 6 to 10 are used when the die hole contains inside corners 3. Stops 11 to 15 are used when the die hole con tains sh arp inside comers.

3

I

2

SMOOTH DIE HOLE CONTOUR

INSIDE CORNERS

SHARP INSIDE CORNERS

Front Spacer Finger Stop Front Spacer Finger Stop Front Spacer Finger Stop No. Width Width No . No. Width 1 1 1/4 1 1/ 2 1 J/4

1 2 J 4

2

5

1 1/2 1 J/1.1. 2 2 1/4 2 1/2

6 7 8 9 10

2 2 1/4 2 1/2 2 J/4

Fig. 13-1 2. Prop ortions of fifteen finger stop s that assure positive stopping of the strip in almost any die design .

3

11

12 13 14 15

147


NO. 1 2 3 4 5

A 8

c

E

F

NO.

A

8

c

D

E

F

,062 .093 ,125 ,156 .187

1.820 2.259 2.635 3.012 3.388

11 12 13 14 15

.125 .187 .250 .312 -375

3/8 7/16 1/2 9/16 5/8

1 7/16 1 19/32 1 3/4 1 29/32 2 1/16

2 1/2 2 25/32 3 1/16 3 11/32 3 5/8

.062 , 093 .125 .156 .187

2.914 3.290 J,666 4.043 4.420

D

.125 1/ 4 21/3 2 1 15/32 .187 5/16 13/ 16 1 3/4 .250 3/8 31/32 2 1/32 .312 7/16 1 1/8 2 5/16 .3?5 1/2 1 9/32 2 19/32

1--.375 I .374

NO.

A

6 7 8 9 IO

.125 .187 .250 .312 .375

c

B

E

F

,062 .093 .125 .156 .187

2.414 2.790 3.166 3-543 3-920

D

2 3/8 15/ 16 7/16 1 3/32 2 9/32 1/2 1: 1/4 2 9/16 9/16 1 13/)2 2 27/32 5/8 1 9/16 3 1/8

Fig. 13·13. Tables of al l necessary dimensions for making finger stops.

13·14. SLOT MACHINING DIMENSIONS

SPRING FINGER STOPS

Slot machining dimensions are tabu lated to correspond with the finger stops in Fi g. 13-13. Machining the front spacer in this way does not affect its function because it is simply a spacer between the die block and stripper plate .

Finger stops occupy a good position to act as stock pushers for keeping the strip firmly against the back gage in its travel through the die. Stock pushers are not ordinarily required for hand feeding because the operator can position the strip against the back gage while advancing it. However, their use eliminates the necessity for side pressure and more uniform strip runs are assured. Stock pushers are indispensible when the strip is to be fed automatically with a roll or hitch feed. Their use makes possible some re duction in scrap bri dge allowance with a saving in material cost. For cut-off dies , in which the edges of the strip become edges of the finished blanks, the use of stock pushers results in more accurate parts. In the following illustrations is shown the method of modifying standard finger stops and of making actuating springs. Applied one way, the spring makes the stop a combination finger stop and stock pusher. Applied another way, the stop becomes a spring-actuated finger stop.

1

I

1- .376

IJ

~ ~ -. 3-77--~--~

,----.............._6~~ c'

_1 I

NO.

A

8

c

D

1 2 3 4 5

1 1 1/4 1 1/2 1 J/ 4 2

1/8 3/16 1/4 5/16 3/8

1/4 5/16 3/8 7/16 1/2

. 064 . 095 .127 .15 8 .189

13-1 5. MACHINING SPRING FINGER STOPS NO.

A

8

c

D

6 7 8 9 10

1 1/2 1 3/4 2 2 1/4 2 1/2

1/8 3/16 1/4 5/16 3/8

3/8 7/16 1/2 9/16 5/8

1/16 3?t2 1 8 5/32 J/16

A

8

c

D

2 2 1/4 2 1/ 2 2 3/4 3

1/8 3/16 1/.J. 5/16 J/8

3/8 7/16 1/ 2 9/16 5/8

1/16 3?t2 1 8 5/32 3/16

NO. 11 12 13 14 15

Fig. 13·14. Tabl es of di mensions for ma chining slot s in front spacer to accommodate the standard finger stops given in Fig. 13·13.

Conventional finger stop A has a slot milled in its underside to retain it in the front spacer and to limit stop travel. Shown at B, the stop is modified by end-milling, or spot-facing, radial pockets in both the heel and the toe of the stop to the same depth as the previously machined slot. Dimensions C of both stops remain the same.

/

B

Fig. 13· 15. Conventiona l (A) and modified (B) fi nger stops.

148


13-16. CONICAL SPRINGS A conical spring, such as the one shown at A, can be compressed until it is completely closed, the coils slipping one into the other. A common application of this principle is the flashlight spring. A small conical spring like the one at A is used for the heavy finger stops with toe dimensions of 3/8 by 3/8 inch. Shown at B is a flattened conical spring, used for the thinner finger stop ranges.

Fig. 13·18. Finger stop in use as a stock pusher.

A

B

Fig. 13· 16. Conical (A) and flattened conical (B) springs for use with spring finger slops.

13-19. SPRING FINGER STOP When the same spring is assembled in the back radi al pocket of the stop, spring pressure acts to keep th e stop away from the strip, as shown. In this view the strip is running through the die with only the automati c stop modifying and limiting its travel.

13-17. SPRING APPLICATION This illustrates the application of a conical spring to a finger stop to convert it into a combination finger stop and stock pusher. Spring A, acting against the face of the radial pocket in the toe of stop B, keeps it in a normally advanced position toward the back gage. Both stop and spring are retained in front spacer C. The strip has been brought against the toe of the stop for piercing holes at the first station. The enlarged view shows the stop, spring, and front spacer with the stripper plate removed.

Fig. 13·19. Conical spring in back radial pocket keeps stop ow from strip.

13-20. SPRING FINGER STOP OPERATION To stop the strip for piercing two holes at the firs t station the stop is pushed in by the operator, compress· ing the spring. Upon release it moves back automaticallr to allow feeding of the strip.

Fig. 13· 17. Method of oppl icat ion of a conical spring to a finger stop making it a combination fin ger slap and stock pusher.

13-18. STOCK PUSHER OPERATION The stop has now been retracted by the operator, compressing the spring to allow the strip to advance against the automatic stop . Releasing the stop causes the spring to push the strip firmly against the back gage. It now acts as a stock pusher until all blanks have been removed from the strip. When a new strip is started it is used as a finger stop again.

Fig. 13·20. Spring finger stop is pu shed in by op erator to stop st i:. for first piercing operation.


149

13-21. DIMENSIONS OF RADIAL SLOTS Tabulated are machining dimensions for applying radial pockets to the line of finger stops described in Fig. 13-13. These can be end-milled, or spotfaced using a simple drill jig with guide bushings .

8

A

STOP NO'S

1, 2, 3, 4-, 5'

6, & 11 7' & 12 8, & 13 9, & 1410, & 15

A

B

• 090 .100

,220 .211 .203 .194.185

.uo

.120 .130

13-23. CUT-OFF DIES When are finger stops not needed in a die? For most cut-off dies, finger stops are not required. Illustrated is a simple cut-off die for producing rectangular blanks. In operation the end of the strip is advanced until it projects slightly past the cutting edge. Tripping the press trims the end of the strip square. The strip is then advanced against stop A, which also backs up the cut-off punch to prevent deflection while cutting. No finger stop is needed because trimming the end of the strip prepares it for register against stop A.

A

B

stock pushers. Thus, the strip is located against the back gage as early as possible in its travel through the die.

Fig. 13-21. Table of machining dimensions for apply in g radial poe· kets in finger stops of Fig. 13·13.

13-22. MULTIPLE STOPS AND STOCK PUSHERS This practical application is a four-station progressive die for producing pierced and stamped links. The two outside finger stops have been assembled to act as stock pushers as well. The center stop was assembled as a spring finger stop to reduce excessive drag on the strip. When a number of finger stops are used, only the end ones need be usually assembled as

( I

I

\

)

'·

Fig. 13·22. A lour-station progressive die uti! i zing two stock pushers an d a spring linger stop.

Fig. 13·23. Cut·ofl die in which linger stops are not required

Section 14

HOW TO DESIGN AUTOMATIC STOPS the strip has been advanced toward the left. Previously blanked strip edge D contacts the toe of the automatic stop, moving it to its extreme left position as shown , "setting" the stop. Descent of the press ram causes the square-head set screw 5 to raise the stop toe to the position shown in section view C. Now, the tension spring 3, acting at an upward angle, turns the stop to the position shown in view B. When the press ram goes up the toe of the stop falls on top of the scrap bridge, allowing the strip to slide under it. After the scra p bridge has passed completely under it, the toe drops to the top surface of the die block, acted upon by sprin g 3. Now the stop is ready to be reset upon contact of the next blanked strip edge. These motions occur at extremely high speeds . On fast runs the motions cannot be followed by the eye. Six parts make up the stop assembly. They are: 1. Automatic stop 2. Fulcrum pin 3. Tension spring 4. Spring post 5. Square-head set screw, usually Y-t in. diameter 6. Jam nut. As shown in the inset of the pictorial view, the hole for the fulcrum pin is taper-reamed from both sides to allow rocking. The slot in the stripper plate is machined angularly to allow stop movement. It is no machined entirely through the stripper plate except a: the toe and opposite the fulcrum-hole portion fo: strength.

Automatic stops, or trigger stops as they are sometimes called, register the strip at the final die station . They differ from finger stops in that they stop the s trip automatically, the operator simply keeping the strip pushed against the stop in its travel through the die. For this reason they are always used when an ope rator is to feed the strip by hand. Automatic stops can be made of cold-rolled steel or machine steel, cyan ide hardened, but when long runs are anticipated they should be made of tool steel, hardened after machinin g. Design considerations include: 1. Fast, positive ac tion under high-speed, high shock conditions. 2. 'linimum machining of the stripper plate for s trength. 3. Sturdy, "gadget-free" design. Automatic stops perform grueling service in operation, and weak design can be a source of trouble. Illustrated are seventeen standardized automatic s tops wi th dimensions tabulated to aid the designer in selecting the ri ght one for the conditions encountered. In addition , general rules are outlined to help in the correct application of these die components . This materia l further explains Step 9 in Section 5, "Fourteen Steps to Desi gn a Die."

14-1. SIDE-ACTING STOP Taken together , two plan views A and B, with a common side section-vie w C, illustrate the operation of a conventional side-acting automatic stop. At A 150

HOW TO DESIGN AUTOMATIC STOPS

151

B

A

c Fig. 14·1. Typical side-acting automati c stop .

14-2. STOP HOLDER · Another method of applying a side-acting automatic stop is to confine the stop in a holder. Here are the fe atures of this construction: 1. The holder can be easily hardened to provide ong life 2. Very little machining of the stripper plate is equired 3. The stop is a self-contained unit, and it can be quickly removed and used in several dies 4. There is no post and exposed spring. Instead, the stop has husky parts and simple, clean lines . View A shows the automatic stop "set" and ready fo r blanking of the hole. At view B the press has descended, releasing the stop and causing it to swing above the scrap bridge. The pictorial view shows stop construction. Stop 1 fits in a tapered slot in holder 2, aeld by fulcrum pin 3. Compression spring 4 provides e required movement. As in Fig. 14-1 a square-head set screw 5, locked by jam nut 6, is applied to the punch holder for operating the stop. In this case the

fulcrum-pin hole is taper reamed from one side only to allow the spring to provide side thrust, as well as up and down movement.

14-3. END-ACTING STOP The same type of stop can be designed as an endacting automatic stop. End-acting automatic stops are easier to standardize because they don't have the great range of lengths required in side-acting stops. The primary modification is an end-milled slot instead of a tapered hole to engage the fulcrum pin . Views A and B show the stop "set," the strip having pushed it back to its maximum left position. Descent of the press ram causes the square-head set screw to turn the stop to the position shown at view C. The spring has now pushed the stop toward the right, the end-milled slot allowing movement. It is obvious from this view that when the upper die goes up the toe of the stop will drop on top of the scrap bridge, allowing movement of the strip toward left until the toe is again engaged by the strip. View A is a plan view of the die, while

HOW TO DESIGN AUTOMATIC STOP

152

2 Fig. 14-2. Side-acting automatic stop that is incorporated into a holder.

views B and C are section views showing operation of the stop. Dimension 0 is the sum of the following: 7'2 Feed 1 Scrap Bridge Allowance 0.010 inch The allowance causes the strip to be stopped 0.010 inch past its required position. Pilots, engaging in previously pierced holes, bring the strip back this amount for final accurate location before blanking occurs .

14-4. SPRING PLUNGER Using a square-head set screw for actuating automatic stops is a time-honored practice that usually works well. One disadvantage is that the set screw must be backed up practically every time the die is sharpened by the amount removed from punch and die members. Many automatic stops have been smashed by the set screw through failure to retract it sufficiently after die sharpening. View A shows a Vlier spring plunger, applied as stop actuator. These are availc.ble from Vlier Engineering Co. The spring plunger has been backed up by a socket lock screw, although a

jam nut would be equally effective. The spring-loa ·,.:: toe of the Vlier plunger actuates the automatic s: = The heavy series of these standard components sho-= be used to assure positive action. The view at B sl:: -s the same die in closed position after repeated sh a.?=!ting. The spring plunger has not been reset in any .-a After actuating the stop, the spring loaded end re r.:.:=s harmlessly as shown.

14-5. STRIPPER PLATE THICKNESS Automatic stop proportions can only after we know what stripper plate thickness wi used. The correct value is found by the formula: A=

w+ 2T

30

In which: A = Thickness of stripper plate W = Width of strip T = Strip thickness Shown in Table 1 are stripper plate thickness~ for representative strip sizes. Table 2 gives ec mended commercially available plate thicknesses it corresponds, for practical purposes, with Tab ~ -


153

c A

B Fig. 14-3. Typical end-acting automatic stop.

2 A

STRIP

A

.225 . )25 .425 .525

X ) X 6 X 9 X 12

-350 .450 .550 .650

1/8 1/8 1/8 1/8

X X X X

3

6 9 12

3/8 1/2 5/8 3/4

6 9 12

.475 .575 . 675 .775

)/16 J/16 J/16 3/16

X X X X

3 6 9 12

1/2 5/8 3/4 7/8

1/4 1/4 l/4 1/4

X ) X 6 X 9 X 12

.600 • 700 .800 .900

1/4 1/4 1/4 1/4

X X X X

3 6 9 12

5/8 3/4 7/8 1

5/16 5/16 5/16 5/16

X ) X 6 X 9 X 12

.?25 .825

5/16 5/16 5/16 5/16

X X X X

6 9 12

3

3/4 7/8 1 1 1/8

X ) X 6 X 9 X 12

1/8 1/8 1/8 1/8

X ) X 6 X 9 X 12

3/16 3/16 3/16 3/ 16

B Fig. 14·4. Actuating an automatic stop with a spring plunger.

A

STRIP 1/ 16 1/16 1/16 1/16

1/16 1/16 1/ 16 1/16

X X X X

3

.925

1.025

1/4 ) /8 1/2 5/8

Fig. 14·5. Tables of stripper plate thicknesses for representative strip sizes (1) and corresponding commercially available plate thicknesses (2).

154


I I II

il_ :

: I

Jl :

()

·II Ill

/

/

(

A

II I

\ "

Fig. 14·6. Proportions for six standard automatic stops.

.....-,_,... f:

I

"-

\

II

I I I LJ / .......__r_...

g

()


155

From this table the designer can quickly select correct stripper plate thickness for the conditions facing him. For example, if strip 1/8 inch by 5 inches is to be run, select the 1/ 8 by 6 size listed in the table and use a 1/ 2 inch stripper plate thickness. For 3/ 32 by 4 inch strip, use the value given for 1/ 8 by 3 inch strip given in the table , and a 3/ 8 inch stripper plate thickness can be used safely. When in doubt as to correct corresponding size, use the next thicker plate. Of course, these are minimum thicknesses for adequate strength. Other factors may cause the designer to choose thicker plate. For example, if the fulcrum pin of the automatic stop is to be retained in the stripper plate, the 1/ 4 inch thick plate may be considered thin and a 3/ 8 plate used instead.

14·7. DIMENSIONS OF STOPS All necessary dimensions are given for making automatic stops ranging from Nos. 1 to 6. From this table the designer can apply dimensions, or the automatic stop can be specified by number. If a side-acting stop like the one shown in Fig. 14-1 is to be designed, it can be given the same general proportions.

14-8. DIMENSIONS OF HOLDERS All necessary dimensions are supplied for holders to be used with stops Nos . 1 to 6. These holders would be made of machine steel unless unusually severe duty is anticipated, in which case they would be made of tool steel and heat treated.

14-6. STANDARDIZED STOPS AND HOLDERS Proportions of these six standardized automatic stops enable ready selection for almost any die design as they can be used in stripper plates varying in thickness from 1/4 to 7/ 8 inch, in increments of 1/ 8 inch. Note that first, the correct stripper plate thickness is selected from Table 2 of Fig. 14-5. Then, from this table, select the corresponding stop to use.

14-9. HOLES IN STRIPPER PLATES This table gives dimensions for machining the holes in the stripper plate to receive the automatic stop assembly. This type of automatic stop is a self-contained unit and it can be removed quickly from the die by simply removing two screws.

/ s__i i i ~ () 8 ---------;~!

T

0

c

H B c 0 E F I G 1/lt 4 ll/J2 1/ 4 1 Jf~6 25/J2 1 3/8 J/ 16 1/ 4 1 I/ 4 1 7/16 1/ 4 1/lt 15/ 16 It J/ 16 3/8 4 J/8 1/lt 1 3/32 13/ 32 1/ 4 1 9/16 5/16 1 J/8 7/16 5/ 16 1 15/ 32 1 ll/ 16 3/B It 9/16 5/16 1 1 1/ 4 5 4 13/ 16 5/16 1 15/ 32 15/ 32 5/16 1 17/ 32 1 13/ 16 7/ 16 6 5/16 1 11/ 16 1/ 2 5/ 16 1 5/B 1 15/ 16 1/ 2 5

NQ

A

I

1 2 J 4

NO. M 1 J/ 16 Dr. 3/ B Dp, 45 C/s1nk 1/ 16 Dp. 2 3/ 16 Dr. 3/8 Dp, 45 C/s1nk 1/ 16 Dp. 3 3/ 16 Dr. 3/ 8 Dp . 45 C/ s ink 1/ 16 Dp . 4 3/ 16 Dr . 3/8 Dp . lf5 C/s1nk 1/16 Dp . 5 3/16 Dr, 3/8 Dp , 45 C/s1nk 1/ 16 Dp. 6 J/16 Dr, J/8 Dp .

J

I

J K 1/8 9/ 32 a. 1 8 5/ 32 9/32 a. 1/ 8 5/J 2 9/32 a. 3/ 16 7/ 32 ll/ 32 a, 3/ 16 7/ 32 13p 2n. 3/ 16 7/ 32 7 16 R, ~tfi2

L J/16 1/4 1/ 4 9/32 5/ 16 3/8

N 60

p 1/ 2 R.

Q 30°

R

s

1/ 16 R.

J / 64 R.

1/8 R.

T 1/ 16 R.

21/32

60

5/ 64 R,

1/ 2 !!,

300 3/64 R,

1/8 R.

5/ 64 !!.

1) /16 31/32

0

u

6 1/ 2°

5/6 1f R.

1/2 a.

300 3/ 64 a.

1/8 R.

3/ 32 R.

6 1/ 2°

) / 32 R.

1/2 R.

300 3/64 a.

5/J2 a .

7/64 R.

1 1/ 8

?0

3/ 32 a.

1/2 !!.

30 ° 3/64 R.

5/ 32 R,

1/ 8 R.

1 9/ 32

7 1/ 2°

3/32 a .

1/2 a .

30° 3/64 R.

5/32 a .

5/32 R.

1 7/ 16

Fig. 14-7. Tables of dimensions lor making the six standard automatic stops given in Fig. 14-6.


156

NO

B

A

1 1/4 21/32 2 3/8 1)/16 3 l/2 31/32 4 5/8 1 1/8 5 3/4 1 9/)2 6 7/8 1 7/16

1 l 1 1 1

c

0

1 1/8 l/ 4 3/8 1/2 5/8

2 l /8 3/8 l/2 7/8 3

2 2 2 2

p

Q

1

33°

7/32

1/8

2

33°

17/64 3/16

)

3)0

17/ 64

1/4

4

)30

5/16

5/16

5

J3"

ll/)2

3/8

6

3JO

J/8

NO. 0

E F G H I J K 1 1 1/2 1/8 1/8 l/4 1/2 3/4 l 1/8 9/16 13/16 1/8 1/8 1/4 l 5/8 l l /4 5/8 29/32 1 1)/16 1/8 1/8 l/4 l 3/8 ll/ 16 31/32 1 15/16 5/)2 5/32 5/ 16 1 1/2 J/4 1 J / 32 2 3/16 5/)2 5/32 5/16 1 5/8 13/16 l 5/J2 2 5/16 5/J2 5/32 5/16

s

R 1/32

X

45°

3/32

T 17/64 Dr.-13/32 C' bore 1/ 4 Dp ,

1/32

X

45°

1/ 8

17/64 Dr.- 1)/32 C' bo re

l /)2

X

45 °

1/8

21/64 Dr.-15/)2 C'bore

1/)2

X

45 ° 3/16 21/64 Dr.-15 / 32 C' bore

1/)2

X

45 ° J/16

7/16 1/)2

X

45° J/16 25/64 Dr.- 19/ 32 C' bore

25/64 Dr .- 19/)2 C'bore

L 5/16 ll/)2 ll/)2 13/32 15/)2 1/2

u

) /16 Dr. )/32 Dp . 4S0 C' sink 3/64 Dp . 1/4 Dp, )/16 Dr. 3/32 Dp , 4SC C' sink 3/64 Dp. 5/16 Dp . )/16 Dr. 3/)2 Dp. 45"C's1nk ) /6 4 Dp , 5/16 Dp. 3/16 Dr. 3/32 Dp. 45"C's1nk J/64 Dp . 9/16 Dp . )/16 Dr. J/)2 Dp . 4SC C' sink J/64 Dp. 9/16 Dp. )/16 Dr. J /)2 Dp. 45"C's1nk J/ 64 Dp.

Fig. 14-8. Tables of dimens ions for holders to be used with the six standard automatic stops.

NO.

A

B

1 2 J 4

1. 4687 1.5625 1. 7187 1. 875 0 2. 0000 2.1562

1. 3750 1.4687 1.6406 1. 7656 1. 8906 2. 0625

5 6

c 1 1 1 1 1

1 1/8 1/ 4 J/8 1/2 5/8

D

E

5/ 16 J/4 5/16 13/16 11/)2 29/J2 1)/) 2 )1/) 2 13/)2 1 J /)2 7/16 1 5/)2

N M 23/64 5/16 l )/)2 ll/)2 )/8 7/16 1/ 2 7/16 9/16 15/32 17/32 5/8

F 1 1/2 . 1 5/8 1 1)/16 1 15/16 2 J/16 2 5/16

G 1/4-20 1/4-20 5/16-18 5/16 - 18 J/8-16 )/8 - 16

Tap T:.p Tap Tap Tap Tap

Fig . 14-9. Table of dimensions for machini ng automatic stop as sem· bly holes in the stripper pi ate.

157


14-10. SET SCREW LOCATION Tabulated are dimensions A between automatic stop and actuating square-head set screw. By standardizing the position of the actuating screw, more uniform results are assured.

STOP NO.

A

1 2

1 1/8 1 J/16 1 1/4 1 5/16 1 ) /8 1 7/16

3 4

5

6

14-11. TOE LENGTHS Toe lengths A are given for all stops incorporating the variations described in Fig. 14-12. We now have 17 standardized automatic stops, many of which vary only in respect to dimension A.

STOP NO.

A

1

25/)2

2 2-A

I5/I6 1

J ) -A J-B

1 J/)2 1 5/)2 1 7/)2

4 4-A 4-B 4-C

1 1/ 4 1 5/16 1 J/8 1 7/16

5-B

5-C

1 1 1 1

6 6-A 6-B

1 ll/16 1 J/ 4 1 1)/16

5

5-A

=ig. 14·10. Ta bulated dimensions (A) of distance between automatic sop and square·head set screw for the six standard automatic stops.

:.-

..

15 / )2 17/32 19/)2 21/)2

Fig. 14·11. Tabulat ion of toe length (A) dimensions •

14-12. BACK GAGE THICKNESS Still another factor mu!';t be taken into consideration ?ihen specifying toe length C of Fi g. 14-7 and A of Fig. 14-11 . This is the thickness B of the back gage and front spacer, because in Table 2 of Fig. 14-5, the same stripper plate thickness can be used for more than ne strip thickness. For example, a stripper plate 3/ 8 ·nch thick is ~sed for 1/16 by 6 inch strip. But it is also used for 1/ 8 by 3 inch strip which would require

a thicker back gage and front spacer, raising the stop. In this table further automatic stop numbers are applied to allow for these variations. For example, stripper plate thickness 1/2 inch can have a spacer thickness B of 1/ 8 inch which calls for stop No . 3. It may also have a spacer thickness of 3/ 16 inch in which case stop No. 3-A would be used. Still another spacer thickness is 1/ 4 inch, with which stop No. 3-B would be used.

STRIPPER PLATE THICKNESS 3/8

1/4

8

NO.

8

1/8

1

1/8 )/16

2-A

2

7/8

3 /4

5/8

1/2

NO.

A

8

NO.

8

NO .

8

NO.

1/8

J J-A ) -B

1/8 J / 16 1/4 5/16

4 4-A 4- B 4- C

J/16 1/4 5/16 J/8

5-A

)/16 1/4

8

NO.

5

1/4 5/16 J/8

6· A

5-B 5-C

Fig. 14· 12. Modificati ons of six standard automatic stop numbers to allow for varying thicknesses of back gage and front spacer.

6 6-B

158


14-13. FULCRUM PIN

14-15. PIN STOP

Dimensions are given for fulcrum pins for all stops. Fulcrum pins are ordinarily made of cold rolled steel, but they would be made of drill rod for long runs.

Trigger type automatic stops previously described are used for all but very wide blanks. Wide blanks , run in slow presses, can be located by a simple pin stop pressed into the die block. In operation the strip clings around the blanking punch and is removed from it upon c_o ntact with the underside of the stripper plate . The operator applies pressure against the strip tendin g to move it toward the left so that, as it is released , it falls with the scrap bridge on top of the pin stop to allow feed ing. A sight hole should always be applied to the stripper plate so that the operator can see stop action.

STOP NO.

A

8

1 2 3 4 5 6

7/8

)~2

1

1 1 1 1

1/8 1/4 J/8 1/2

1 8

1/8 3/16 J/16 J/16

Fig. 14·13. Table of fulcrum pin dimensions.

14-14. SPRING DIMENSIONS Outside dimensions of springs used in these automatic stops are now given. All stops use the same size spring, but pressure can be varied by using different wire diameters.

Fig. 14·15. Simple pin stop for wide blanks run in slow pres se s.

Fig. 14·14. Spring dimensions for use in standard automatic stops.

Section 15

HOW TO DESIGN STRIPPERS j

Stripper plates remove the material strip from around blanking and piercing punches. Severe adhesion of strip to punches is characteristic of the die cutting process. Because of their low cost, solid strippers are the most frequently used type, particularly when running strip stock. Spring strippers, though more complex, should be used when the following conditions are present: 1. When perfectly flat, accurate blanks are required, because spring strippers flatten the sheet before cutting begins. 2. When blanking or pierci'\g very thin material, to prevent uneven fracture and rounded blank edges. 3. When parts are to be pressed from waste strip left over from other operations, spring strippers provide good visibility to the operator for gaging purposes. 4. Because stripping occurs immediately, small punches are not as subject to breakage. 5. In secondary operations, such as in piercing dies, increased visibility provided by spring strippers allows faster loading of work and increased production. Stripper plates may be made of cold-rolled steel if they are not to be machined except for holes. When machining must be applied to clear gages, the plates s hould be made of machine steel, which is not as subject to distortion. Illustrated and described in this section are eighteen methods of applying stripper plates and their components. These methods further explain Step 10 in Section 5, "14 Steps to Design a Die."

back gage and front spacer with four button head socket screws. Two dowels accurately locate the stripper plate in relation to the die block and back gage. A small, short dowel locates the other end of the back gage to the stripper plate. Notch B is machined in the stripper edge to provide a shelf for starting new strips through the die.

15-1. SOLID STRIPPERS Here is the most common method of applying a solid stripper. Plate A, machined to receive blanking and piercing punches, is fastened in position on top of the

Fig. 15·1. Common method of applying a solid strip per.

159

160

HOW TO DESIGN STRIPPE R

Fig. 15-2. Alternate design of solid stripper used now only for very small dies.

F ig. 15-3. Stri pper plate for secondary operation s.

15-2. ALTERNATE METHOD An alternate method of designing a solid stripper is to make it thicker and machine a slot in its under· sideslightlylarger than strip width . In its travel through the die, the strip is located against the back edge of the slot. Once widely used, this method has now become obsolete except for very small dies.

kept short for ri gidity. The stri pper plate is c oun :e:\drilled for clearance . At C small punches may :~ guided in hardened bushings pressed into hol es - :;. chined in the stripper.

1.5-3. SECONDARY OPERATIONS For secondary-operation work, stripper plates are fastened on top of two guide rails set at either side. This die pierces two holes in a rectangular blank. Ga ge pin A locates the blank endwise, while it is confin ed sid ewise between the guide rails . The stripper plate is reliev ed at the front to provide a shelf for easy inserti on of the bl ank. The die block is relieved at the front to provide finger room.

15-4. MACHINING PUNCH OPENINGS Three methods are us e.d for machining punch openings in the stripper plate. At A, a 1/8 inch straight land is applied from the bottom of the plate. Above the land, angular relief is provided to cle ar the punch radius when the punch is lowered in die sharpening. At B the cutting diameter of the small punch is

15-5. SPRING STRIPPERS Views A, B, and C illustrate the operation o: : sprin g stripper plate . Springs , arranged around -~ blankin g punch, provide stripping pressure. f stripper bolts, located at the corne rs , limit s ·:;.::e travel. View B shows the die in open position , view C shows the die as it would appear at the bo:: of the press stroke. Springs have been compress::-:. ready to strip the material from a round the punch :: movement of the punches. View A s hows the holder, blanking punch, and punch plate invertei ~ they would appear in the upper right hand view o: die drawing. For large dies, cost of the die set becomes ic,.. tant. So the stripper plate corners are beveled to co="die pos ts and guide bushin gs, thereby a llowin g use : a smaller die set. Springs are retained in pocl~ counterbored in the punch holder and in the sti ,_ :.plate. The holes are countersunk 1/ 8 inch ':- _:: degrees in th e punch holder and 1/ 16 inch by degrees in the stripper to guide the sprin g coi c:o small hole is drilled completely through the . ~ holder and stripper plate while the two are c a=:;r.: together. This hole provides for enga gement of counterbore pilot. 0

-=

0

HOW TO DESIGN STRIPPERS

A

161

c

B Fig. 15·4. Three typ es of punch openings for stripper s.

\

A

c

B Fi g.. l5-5. Typical spring strippe r.


162

15-6. SPRING PILOTS

15-8. SHORT STRIPPER SPRINGS

You can avoid counterboring the stripper plate to retain springs by the use of spring pilots . These can be made to su it conditions, or they can be purchased from Ri chard Brothers Punch Di v. of Allied Products Corp., Detroit, Mich., who have developed a standardized line of these components.

When stripper springs are short, it is not necessary to counterbore the stripper plate. The springs are retained, either by holes in the punch plate or in counterbored holes in the punch holder .

Fig. 15-6. Spring pilot retains strippe r pl at e spring.

Fig. 15-8. Short stripper spring does not requ ire hol e in stripper ma intai ning posi t ion.

,

15-9. SP RINGS RETAIN ED BY STRIPPER BOLTS 15-7. MACHINING THE PUNCH PLATE When a punch plate is used to retain piercing punches, holes are bored through the punch plate to hold stripper springs. This construction avoids counterboring the punch holder of the die set.

Fig. 15-7. Hole bored in punc h plate re tains stripper spring.

For medium-production dies, springs around stripper bolts as shown. This recommended for long runs because of on the stripper bolts, and because of the the bolts in the event of broken s prings.

can be applie: method is n · increaseq wea: need to r~mo ·2

Fig. 15-9. Spring retaine d by strippe r bolt is used in med it..--: duction die.

HOW TO DE SIGN STRIPPERS

15-10. APPLYING STRIPPER BOLTS For severe applications stripper bolts are better ap plied with their bearing shoulders confined in short counterbored holes in the stripper plate for strength . The counterbore is usually made 1/ 8 inch deep and a press fit is specified for the diameter of the hole.

163

stripper usually extends l / 32 inch past the faces of cutting punches to flatten the strip properly before cutting occurs.

15-12. "STRIPPIT" SPRING UNITS "Strippit" spring units are self-contained assemblies tha t allow removal of the stripper plate without dismantling springs. They are available from WalesStrippit Corp., North Tonawanda , N.Y. Socket cap screws, or socket flat head screws for thin plates , retain the stripper plate to the "Strippit" units . Because pressures are self-contained, thinner stripper plates can be used and stripper bolts are not required.

Fi g. 15-1 0. Method of apply in g stripper bolt for severe appl ications .

15-11. SPACER WASHERS When punches are sharpened, spacer washers are applied under stripper bolt heads to main tain correct :elationship between the underside of the stri pper plate an d the faces of blanking and piercing punches . The

Fig. 15-12. "Strippit" spring un it allows removal of strippe r without disman t ling springs .

15-13. ALTERNATE METHOD Another method of applyin g stripper pla tes to "Strippits" is to insert short socket cap screws in the units. The cap screw heads engage holes in the stripper plate to prevent lateral movement. Stripper bolts limit travel.

15-14. RUBBER SPRINGS For medium and low production dies, rubber springs may be used . These rubber components are available from Richard Brothers Punch Di v. of Allied Products Corp., Detroit, Mich. Dowel pins, pressed into the stripper, retain the rubber springs in position.

15-15. FLUID SPRINGS =ig. 15-11. Washer s are ap pl ied und er str ipper bolt head when un ches are sharpened.

Where extremely high stripping pressures are re· quired, fluid springs reduce the number of spring units required in the die , an important factor where space

HOW TO DESIGN STRIPPER

164

Fig. 15·13. Alternate method of applying "Strippit" spring unit to str ipper.

Fig . 15·15. Fluid springs are used where extremely high stri pp i- ; presures are required.

Fig . 15· 14. Rubber spr ing for medium and low produ ction dies .

is limited. F luid springs are filled with an emulsion of silicones in oil. The one illustrated is available from from Wales -Strippit Corp. , North Tonawanda, N.Y.

Fig . 15-16. Type standard springs.

of fluid

spring that

is

interchangeab le ~

15-17. INVE RTED DIES 15-16. TAYLOR FLUID SPRINGS Another type of fluid spring is made interchangeable with some sizes of standard springs. These are available from Taylor Devices Inc. , North Tonawanda, N.Y. Both the Wales and Taylor liquid sprin gs are fastened to the die by threadin g their shanks into holes tapped in the die set.

In inverted dies the blanking punch is fastene · the lower die holder of the die set, instead of o ·· punch holder as in conventional dies. In such app · =tions the spring stripper is reversed. Reversi ng · - _ stripper plate does not alter applic ation of the co- ponen ts previously described except -that they ::~: inverted also.


165

inch, the force for this deflection will be twice the listed amount (as the listed amount is for 1/ 8 inch deflection for that size of spring). To this is added the force for the first 1/ 8 inch of working compression;

Fig. 15·17. Typical inverted die.

15-18. STRIPPING FORCE When spring strippers are used it is necessary to calculate the amount of force required to effect stripping. Stripping force is found by the formula:

r Where:

p =Lx

r

x

A

855

L :: Length of cut. In piercing operations this is the the sum of the perimeters of all perforator faces.

= Thickness of stock P = Force, in pounds, to effect stripping.

T

The constant 855 was derived from an empirical Lx T formula: p =0.00117 This formula has been in use for many years in a number of plants and it has been found to be satisfactory for most work. The constant 855 (the reciprocal of 0.00117) simplifies calculations. These formulas are for "full stripping". In blanking dies and progressive dies in which only strips are to be run and thin, weak scrap bridges are present in the scrap strip, the calculated figure may be reduced somewhat, depending upon the number and extent of the weak areas. But the value of P should never be reduced in applications where there is any possibility of scrap pieces from other operations being stamped in the die. After the total stripping force has been determined, the stripping force per spring must be found in order to es tablish the number and sizes of springs required. Force per spring is listed in manufacturers' catalogs in terms of pounds per 1/8 inch deflection. In some catalogs it is given in pounds per 1/ 10 inch deflection, and must be converted to pounds per 1/ 8 inch deflection by simple proportion. Three types of spring deflection must be taken into consideration. Illustrated at A is initial compression, usually 1/ 4 inch, which compresses the springs to apply a preload. At 8 is shown working compression, which is further deflection of the springs while work is performed. At C is illustrated grinding compression, usually 1/ 4 inch, which is the amount allowed for sharpening punches during the life of the die. If a spring 11/2 inches in diameter by 6 inches long is tentatively selected, and initial compression is 1/4

B

c Fig. 15-18. Three types of spring deflection which must be con· sidered when determining stripping force.

no more force is added because too high a value would result, and the force would fade away near maximum travel. Should the working compression be less than 1/ 8 inch, say 1/ 16 inch, only one-half of the listed force would be used in the calculation . For example: Listed force per 1/ 8 inch compression:

20 pounds

40 pounds 1/ 4 inch initial compression: (2 x 20) 1/ 16 inch working compression: (1/2 x 20)10 pounds 1/ 4 inch grinding compression: (2 x 20) 40 pounds Total force per spring:

90 pound s


166

This value represents the total amount of force exerted by the compressed spring after 1/4 inch has been removed in sharpening. It is the maximum force and the value should be used in any calculation of strength of members. To determine the number of springs required to effect stripping, we must know the force exerted by each spring before sharpening. Therefore, referring to the example: Lis ted force per 1/8 inch com pression:

assembly consists of knockout plate, A knockout rod B, and stop collar C. At the bottom of the press stroke, the blanking punch has removed the blank from the strip and inserted it into the die block, raising the knockout assembly.

20 pounds

1/ 4 inch initial compression: (2 x 20) 40 pounds 1/ 16 inch working compression: (1/2 x 20) 10 pounds Force per spring:

50 pounds

The number of springs required is found by dividing the total stripping force by the force per spring. If the number arrived at is out of proportion to the die, use fewer and larger springs, or perhaps more springs of smaller size. Or pressure may be increased by applying more initial compression. Manufacturers' catalogs list the maximum amount of compression to apply, and their recommendations should be followed. In general they suggest: 1. For high-speed work both "medium pressure" and ''high pressure'' springs should not be deflected more than 1/4 of their free lengths 2. For heavy, slow-moving presses use "medium pressure" springs with a total deflection not to exceed 3/ 8 of their free lengths.

KNOCKOUTS Knockouts remove, or strip completed blanks from within die members. They differ from stripper plates in that stripper plates remove the material strip from around punches. There are three types of knockouts: 1. Positive knockouts. These eject the blank upon contact of the knockout rod with the knockout bar of the press. 2. Pneumatic knockouts. These are actuated by an air cushion applied under the bolster plate of the press. 3. Spring knockouts. These employ heavy springs as the thrust source. The knockout plate or block in contact with the part is usually made of machine steel, but would be made of heat-treated tool steel when it also performs a forming operation. Knoc kouts can be applied in two ways. In the first, Direct knockouts, the force is applied directly from source. In th e second, Indirect knockouts, the force is applied through pins arranged to clear other die components, such as piercing punches. Illustrated are 21 methods of applying knockouts to dies, as well as details of their construction, and methods of finding the center of stripping force for correct design.

Fig. 15-19. Inverted blanking die with positive knockout.

15-20. STRIPPING THE BLANKS Near the top of the press stroke the knockout rod contacts the stationary knockout bar of the press . Continued ascent of the upper die causes the knockou to remove the blank from within the die cavity. If th e job is run in an inclined press, the blank falls to th e rear of the press by gravity. Thin blanks may be blown to the rear of the press by air. Blanks produced fran: oiled stock tend to cling to the face of the knockou . When this condition is present, a shedder pin applied to one side of the knockout plate will break the adhesi or: and free the blank. Three types of shedder pins were illustrated in Fig. 8-15 in the section on Blanking Punches.

Fig. 15-20. Knockout removes blank near top of press stroke .

15-19. OPERATION OF A KNOCKOUT Taken together, Figs. 15-19 and 15-20 illustrate the operation of a positive knockout. This is an inverted blanking die, with the blanking punch fastened to the lower die holder of the die set, and the die block fastened to the upper punch holder. The knockout

15-21. CENTER OF STRIPPING FORCE Before designing the knockout, the center of stri p ing force must be found. If the knockout rod is no: applied at the exact center of stripping force, the roc will be stressed and possibly bent in operati c::


167

Symmetrical blanks present no difficulty, but when the blank outlines are irregular here is the method to use: Place a sheet of cardboard (board for show cards is best) under the part drawing. In se rt carbon paper between the drawing and cardboard and trace the part

0

0

using a pin or thumbtack. With a trian gle. draw a vertical line directly under th e hole fro m which the blank is s uspended. Turn the blank around and, s uspending it from one of the other holes, draw another vertical line crossing the suspension hole. The intersection of the two lines is the center of stripping force . Suspend the blank from the third hole to provide a check for accuracy.

15-23. SPRING DAMPER

L W*'

In app lyi ng a positive knockout, many designers prefer to provide a relatively weak spring around the knockout rod. This spring is not strong enough to strip the part. It s function is t o prevent unnecessary travel and bounce of the knockout to reduce wear.

KNOCKOUT ROD

P'ili

c=?

0

0

I

Dc=JD

1

B

Fig. 15·21. Ways of determining cen ter of stripping force.

outline, as well as all holes and openings. With scissors cut out a cardboard blank a s shown in the plan view. All holes and openi ngs may be cut out of the blank as shown at A. The blank is then balanced over a point, (a pencil will do). The center of balance is the center of stripping force. Cutting out small holes is difficult, so here is an a lternate method: From the same weight cardboard cut slugs the shape and size of all holes and openin gs. Paste these in position on top of the blank as shown at B. Balancing the blank as before will establish the center of stripping force.

15-22. ALTERNATE METHOD For very large blanks, which would be difficult to balance, pierce three small holes, A, close to the edge of the blank. Suspend the blank from a vertical surface,

Fig. 15·23. Spring around the knockout rod is too weak to strip but prevents need less travel and bounce,

15-24. GUIDING IN THE KNOCKOUT Slender piercing punches may be guided in the knockout by providing hardened bushings pres sed into the knockout plate. Close fits between the knockout and other die components must be maintained .

Fig. 15· 24. Slend er piercing punches are guided by harden ed bush ings in the kno ckou t plate.

15-25. EJECTING CUPS AND SHELLS -ig. 15-22. A,lternate method of determ in in g center of stripping orce .

Positive knockouts may be used to eject drawn shells. In this combination die the upper punch blanks a disk from the strip, and in further descent draws it

168


in to a flanged shell. Lower knockout A is raised by pins actuated by the air cushion of the press, and it strips the shell from around draw punch B. Positive knockout C, actuated near the top of the stroke , removes the shell from within the die and it falls to the rear of the press.

and socket lock screw, prevents adhesion of the part to the knockout fac e.

A

Fig. 15·27. Die in wh ich knockou t is used for form ing or em bo ssing.

A

B

Fig. 15- 25 . Po si tive knockouts ore used to eject drown she ll s.

15·26. TRIMMING OPERATIONS In this trimming die for a previously drawn flanged cup , a positive knockout, relieved to clear the shell body, removes the shell from within the di e hole. Whenever a knockout is used to remove formed or drawn stampings, it should be relieved so that stripping force is applied only near cutting edges to prevent distortion of the parts .

15-28. BOTTOM KNOCKOUTS Bottom knockouts, operated by the press air cushion as in Figs. 15-25 and 15-27, have their pins ap plied in seven ways . At A, pins transmit force from th e face of the air cushion to the underside of the knockout rin g. This method proves suitable for very long press ru ns . The pins are loose and may become lost if the die is removed often. At B, the pins are peened, then machined to form beveled heads to prevent dropping out when the die is removed from the press . At C,

A

8

c

D

E

Fig. 15· 26. Posit ive knock out is relieved so as to apply stripping fo rce ne ar tri mmed edge.

F 15-27. FORMING IN THE KNOCKOUT For som e types of work the knockout provides the final forming operation. This combination die produces a flanged cover by blan ki ng a disk and drawing a shallow fl anged shell. At the bottom of the stroke the knockout, in conjuncti on with the lowe r embossing punch A, embosses a s hal low recess in the part. When knockout plates do fo rmi ng they are made of hardened tool s teel and are backed up by a plate to "spank," or set the form. A shedder pin, backed up by a spring

G

Fi g. 15-28 . Several metho ds of pinning bottom knockout s.

turned heads retain the pins in the die set. The knoc kout rin g has a flange to retain it in the die. At D the ends of the pins are turned down and pressed into the knockout ring, while at E the pins are turned down and threaded into the knocko ut rin g. At F the tops of the pins are turned down and are pressed in to the knockou rin g. The pins are also turned down at their lower ends and pressed into collars. In the up position the collar


seats against the bottom of the die set to limit travel. It also retains pins and knockout ring to prevent loss. At G, lon g, rectangular knockout plates used in bending a nd forming dies are retained in the die set by two or more pins with turned down ends pressed into the knockout bar at the top, and also into the bottom retaining bar.

15-29. SPRING KNOCKOUTS Spring knockouts are used in dies too large for the positive types. Stripper bolts limit travel. One disadvantage is that the blank is returned into the strip and it must be removed subsequently. In so_me progressive dies the blanking station is provided with a spring knockout to return the blank into the strip for further operations.

169

15-31. PRESSURE PINS AND STOP COLLARS The number of pressure pins used and their arrangement depends upon part contour and size. At A, knockouts for round blanks have three actuating pins . At B, blanks with a roughly triangular sh ape are also provided with three actuating pins . As shown at C, blanks which are roughly rectangular, or square , require the use of four pins. There are three ways of applying a stop collar to the knockout rod. At A, a collar is pressed over the end of the knockout rod and retained by a dowel pressed through both. At B, the knocko ut rod is machined to form a solid shoulder. At C a dowel is pressed through the knockout rod. Although often used, this method is not recommended because, should the press not be set up properly, the dowel could be sheared with consequent dama ge to die components.

l

0

Fig. 15-29. Typ ical s pring knockout used in Iorge dies.

h 15-30. INDIRECT KNOCKOUTS The knockouts described so far have all been the direct-acting types. Indirect knockouts are used when piercing or other types of punches are in line with the knockout rod . This illustration shows an indirect

I

'

B

A

(

c

Fig. 15-31. Ar ran gemen t of pressure pin s and stop indirect knockouts .

collars fo r

15-32. GUIDE PINS Slender piercing punches may be guided in the knockout block of indirect knockouts. Guide pins A, pressed into the knockout block, transmit strippin g force a nd also guide the block. They are fitted in hardened bushings B. The knockout plate travels in a recess machined in the punch holder of the die set.

Fi g. 15-30. Typi cal indirect knockout.

knockout with force transmitted through pins to clear a central piercing punch. The knockout plate moves in a recess milled in the upper punch holder of the die set. Through the pins , it actuates the knockout block to push the blanks out of the die hole .

Fig. 15-32. block.

Pins (A) guide and transmit force to th e kno ckou t


170

15-33. AUXILIARY PUNCH SHANK When the press has sufficient opening, an auxiliary punch shank may be fastened to the punch holder of the die set. The knock plate travels in a recess machined in the bottom of this auxilliary shank .

punches a re applied, the spider has three arms to clear the punches. This type is shown at A. For four punches a four-armed spider, at B, would be used. Piercing punches, applied at other than radial locations are cleared by holes in knockout frames such as the one shown at C. The shape of the knockout frame would depend upon the number and arrangement of the punches .

Fig. 15·33. Die in which auxiliary punch shank is fastened to the punch holder of the die set.

15-34. BACKING BLOCKS

Fig. 15-35 . Knockou t plate is of spide r shape to facilitate pie r ci n~ ring-shaped par ts.

In another method, the soft steel backing block A can be machined to accommodate the knockout plate. This die produces ring shaped parts .

~

Q A

8

~ ~ c

Fig. 15·36. Various shapes of spider knockout plates. Fi g. 15·34. Soft stee l back ing plate (A) machined to accommodate th e knoc kout plat e.

15-35. SPIDER KNOCKOUTS When holes ar e to be pierced in ring-shaped parts, the knockout plate ha s a spider shape and the punches are retained between the arms of the spider. On the drawing one arm of the spider is drawn at one side, and a piercing punch at the other.

15-36. SPIDER KNOCKOUT PLATES The number of arms contained in knockout spiders such as the one us ed for the die Fig. 15-35 depends on the number of piercin g punches required . When three

15-37. FLAME-CUTTING KNOCKOUTS One method frequently used to save material is ·: flame cut the spider knockout entirel y through _ backing plate. The spider is removed from the p lc.:~ and then machined thinner to allow up-and-down mo ·cment. Since the knockout pocket is cut comple e :_ through the plate, the pins must be securely faste e: to the spider arms, in this case by pressing and ri ve:· ing their ends. Still another method of applyi ng large spider knoc ::· outs is to flame cut the spider through the pun c:: holder of the die set. A steel die set must be specifiei and the flame cutting must be done by the die se: manufacturer before stress relieving and final accurate machining.

171


the part is returned to the strip for other operations, and removed from the strip at the last station.

Fig. 15-37. Spider knockout plate in this die has been flame cut.

15-38. KNOCKOUT RODS These are the three commonly used methods of securing the knockout rod to the knockout plate. At A the rod end is turned down, pressed into the plate, and riveted over. When heavy knockout pressures exist, the knockout rod is provided with a shoulder to prevent it from sinking into the knockout plate as shown at B. In this method also the end is turned, pressed in, and peened over as in the previous example . At C is shown still another method of fastening heavy knockout rods. The end is provided with a shoulder, threaded into the knockout plate, and prevented from loosening by a dowel pressed through the flange and into the knockout plate. The dowel hole is carried through th e plate, but with a smaller diameter to prevent the dowel from working out in operation .

Fig. 15-39. Knockout plunger (A) conta ined within punch shank operates indirect knockout.

Fig. 15-40. Typical small knockout of the spring-operated variety.

A

8

c

=ig . 15-38. Three methods of securing the knockout rod to the nockout plate.

15-39. KNOCKOUT PLUNGERS Indirect knockouts for small dies may be operated 3Y a knockout plunger A, applied within the punch -hank. Cap B, fastened to the punch shank with socket cap screws, provides an outboard bearin g for the ;mockout plunger and also keeps it confined within :be die.

' 5-40. SPRING KNOCKOUTS Small knockouts may be of the spring-operated ":"a riety. One disadvantage is that the part is returned 1. to the strip and it must be removed as an extra peration. However, the blanking station of some :-regressive dies is purposely made in the above manner;

15-41. SPRING·ACTUATED KNOCKOUTS Spring actuated knockouts may be applied to the lower die in a variety of ways. These are used in progressive dies at bending, forming, and embossing stations. At A the knockout is operated by a spring applied in a counterbored hole in the die holder of the die set. Shown at B the hole is carried through the die set and the spring is backed by a plate fastened in the die holder. This provides greater travel. At C knockout blocks of irregular shape may be held by one or more stripper bolts, and pressure is applied by a spring retained in a counterbored hole in the die holder. 0 shows one method of applying the spring within a spring housing fastened under the die set. This construction is used when considerable travel is required. At E, the spring is held under the die set by a stripper bolt, and pressure is transmitted to the knockout through pins. This design facilitates the use of a very heavy spring when high pressure is required and when the press is not equipped with an air cushion.


172

A

0

B

c

E Fig. 15·41. Various ways of applying spring-actuated knockouts to th e lower die.

Section 16

HOW TO APPLY FASTENERS The subject of fasteners is an important one because these components are applied so frequently and employed in such large quantities. Although small, they perform important functions. In the design of tools and dies, fasteners are often the "weakest link" in the tool and, if they are not selected and applied correctly, they can become the cause of failure of the entire tool or die. In applying fasteners, an experienced designer seemingly follows no rules for size, location , or number. But if two designers were to select and apply fasteners for the same job, their choices would be almost identical. In turn, the checker would approve their selections. Obviously, these men have developed a sense of proportion. When a designer looks over a layout and he

decides that screws are too small, too close together, or too close to edges, he is subconsciously being guided by observations of tool components that failed and had the same proportions. Fortunately, definite rules for application of fasteners can be used by the inexperienced designer or student to avoid many pitfalls. These pitfalls include hardening cracks and breaks, stripped threads, distortion by release of internal stresses, and mis-alignment of holes. By the use of these rules, the less experienced man can avoid trouble and quickly develop a correct sense of proportion.

16-1. DIE FASTENERS In this exploded view of a typical die for producing blanks from metal strip, all fasteners have been shown removed from the components which they locate and hold. From this drawing, it is apparent that fasteners, although small individually, form a substantial portion of the entire tool when taken together.

Fig. 16·1. Exploded view of die showing number of fasteners used.

173

HOW TO APPLY FASTENERS

174

16-2. TYPES OF FASTENERS Illustrated here are the types of fasteners most commonly used in die construction. They are: 1. Socket cap screws 2. Dowels 3. Socket button-head screws 4. Socket flat -head screws 5. Stripper bolts 6. Socket set-screws 7. Allenuts. Less frequently employed types include the following: hexagon nuts , wash ers, studs, rivets, and wood-screws.

2

holes for the screw heads are 1/32 inch larger in diameter than the heads. This clearance has been shown slightly exaggerated at the left in the section view. Obviously, these clearances will allow side shift if the screws are loosened. This is exactly what can happen when a tool is taken apart for sharpening or repair. A small amount of side movement of this nature may be permissible in many mechanical assemblies, but in prec is ion jigs, fixtures, and dies, it could cause serious damage. For this reason, closely fitted pins called d owels are applied to effect accurate relative positionin g. Dowels permit no movement between parts. They can be pressed out for repair, then replaced to restore relative positioning to original accuracy.

4

3

---...,

~-~......:::;;;

-

I

!

'-

~

5

6

Fig. 16·3. Socket cap screws and dowels are used in hold ing the se two blocks toget her.

7

Fig. 16 -2. Types of fasteners used in die construction .

16-3. THREADED FASTENERS When compon ents of any mechanical device must be assembled securely, and must be dismantled occasionally for repair , adjustment, or replacement, threaded fasteners are the most effective. Socket cap screws are most often used in tool work, followed by dowels. Fundamental rules govern application of screws and dowels. Screws are used to hold components together. They are not intended to locate components sideways relative to each other. Study of the illustration will show why this is so. Two blocks are fastened together with two screws and two dowels. Clearance holes for screws are drilled 1/ 64 inch larger in diameter than body diameter of the screws, and counterbored

16-4. TO APPLY FASTENERS The first method considered is shown at A. Screws are applied at two diagonal corners and dowels at th e other two comers. This method is employed for small an d medium-size blocks and plates designed to withstand only small and medium forces . For larger blocks an d where larger forces are encountered, the method show at B should be selected. Screws are applied at all fo ur corners and dowels are offset. When still larger force s are present, a fifth screw is applied to the center of the block, as shown at C.

A

8

c

Fig. 16·4. The number of fasteners depends on the magnitude of the the anticipa ted force.


175

16-5. FLANGED PUNCHES When parts have a projection along the center as in flanged forming punches, two screws and two dowels are applied at opposite corners when punches are short, as at A. For longer punches, four screws are applied at the corners, and dowels are offset, as shown at B. Long punches may be fastened with six screws, C, applied three to each side. Dowels facilitate lateral location and are applied in the same manner as for the punch at B.

A~ 1:~

B

c

1:

-
+

• •

:I -
Fig. 16·5. Method of fastening flanged punches.

:I

positioning of the component. Block B shows screws and dowels positioned properly. Space between dowels has increased considerably. We need to know the safe minimum distances C and D.

16·7. SPACING GUIDE This is an illustrated guide which gives correct minimum proportions for applying holes in machine steel and tool steel parts. You will find it invaluable for checking to determine if correct spacing has been applied in your designs, and in time you will come to recognize good proportions instantly. At A is specified correct minimum spacing of holes applied at corners. Note that holes may be positioned closer to edges of machine steel parts than for parts to be made of tool steel. The extra material applied for tool steel components assures that corners will not crack in the hardening process, if it is properly done. When a hole in tool steel or machine steel is located a greater distance from one edge than in the previous example, it may be positioned closer to the adjacent edge, as shown at B. This condition occurs frequently in the application of screw holes in die blocks and in other tool steel parts.

16·6. SPACING OF FASTENERS Proper spacing between holes and between holes and edges of parts is particularly important for tool steel parts to be hardened. If too little space is allowed, there is a strong possibility of the block cracking in the hardening process. But on the other hand, it is often desirable to have screw holes as close to edges as possible, to keep dowels far enough apart for accurate positioning.

MACHINE STEEL

MACHINE STEEL

L = I 1/ 8 D

L = 1 1/ 2 D H =I 0

TOOL STEEL

TOOL STEEL

L = 11/ 4 D

L =I 1/ 2 D

A

H = I 1/ 8 D

A

8

Fig. 16-7. Guide which gives minimum proportions for the spacing of holes from corners in machine and tool steel ports.

16-8. DISTANCE BETWEEN HOLES

B Fig. 16·6. Ineffective (A) and effective (B) spacing of fasteners.

At A, screws have considerable space between them and outside edges. Also, dowels have adequate space between them and their nearest screw holes. Unfor· tunately, the dowels are too close together for effective

Minimum proportions for positioning adjacent holes having the same size are given at A. Note that diameter 0 on view B applies to the small hole , and that distance L is taken from the center of the small hole to the edge of the large hole. This is the common application of drawing holes for a socket cap screw and its adjacent dowel. Under normal conditions, measure distance L from the center of the dowel to the edge of the cap screw head. For crowded conditions, measure to the edge of the clearance hole for the screw body.


176

One-half of the amount found in 4 is the distance between end holes and part edges. Thus, hole locations are properly proportioned. For example: 1. Five holes are required 2. Length A is twenty inches 3. Twenty divided by 5 is 4. Distance between holes is therefore 4 inches. One-half of four is two . Distance between end holes and part edges is therefore 2 inches.

A

8

I I

v

MACHINE STEEL

L = lD

~--------------- A --------------~~

TOOL STEEL

Fig. 16·10. Applying a row of holes in a bar.

L = 1 1/ 8 D

Fig. 16·8. Minimum proportions for positioning adjacent holes in mac hine and tool steel parts.

16-9. LONG, NARROW PARTS Screws and dowels are applied to long, narrow parts in several ways, At A is shown the most frequently used application. Distances E, F. and G are given in Figs . 16-7, and 16-8. Components to be taken apart for repairs are foolproofed by offsetting one of the dowels as at B. When greater strength is required, a third screw is applied in the center, as at C. However, this addition does not affect positions of dowels. Short, narrow plates may be fastened with a single screw applied at the center. Dowels at each side provide accurate lateral location. This application is shown at D.

A

c D

In deciding upon the number of screws required, consider the size of the details in addition to any forces which will act upon the screws. The component being fastened must be pulled down evenly and squarely. Observe these rules: 1. Kee p dowels as far apart as possible 2. Make sure that the screws hold down the part securely fl at. In this segment of a sectional die, the construction at A is incorrect because screws should act somewhere a long lin e C-C for stability. Shown at B is the correc t application , even though dowels are somewhat closer together .

c

~-----,( /

GJ;~

I ~+

F

B

16·11. FORCE ON SCREWS

1 ~! ~16

~

i*: ~E 8

~ ~~

-$-

+$-I

I ~ -$- -$- J

Fig. 16·9. Ways of app ly ing sc rews and dowels in long narrow parts.

16-10. PROPORTIONS In applying a row of holes in a bar, employ the following procedure:

1. Measure length A 2. Decide upon the number of holes required 3. Divide length A by the number of holes 4. The answer is the distance between holes

c

/

A

c

B

Fig. 16·11. Inco rrect (A) and correc t(B) method of applying fastener s in a die se gment.

16-12. FOOLPROOFING A simple way to foolproof parts which might be reassembled incorrectly in die repair is to reverse the relative positions of dowels. This method is applied to gages A in this piercing die. Obviously, gage positions cannot be reversed accidentally, nor could the gages be assembled upside-down because of the holes counterbored for the heads of the screws.

16-13. SCREWS ON DRAWINGS This is the way screws appear in the pl an and front section views of the representative die . Observe that in the flange of the punch a dowel is drawn at one side


177

and a socket cap screw at the other. The die block is fastened to the die set with long socket cap screws applied from the bottom. The stripper plate, back gage , and front spacer are fastened to the die block with socket button-head screws applied from the top . Double dowels illustrated at the other side of the view provide accurate lateral positioning of components. Observe that stripping load against the screws which hold the stripper to the die block is equal to stripping load against screws which hold the blanking punch. When only two screws and two dowels are employed to hold and locate the blanking punch, make the screws larger in diameter than those in the die block where a minimum of four screws are always employed. Compare holding strengths as given in a manufacturer's catalog. In general , screws one size larger, will have to be employed to realize approximately equal holding strength.

A

Fig. 16-12. Simple method of foolprooling back gages (A) to assure correct positioning upon reassembly .

0 0

©

@

0

0

@

0

Fig. 16-13. Method of application of and appearance of fasteners in a typical die drawing.

16-14. HOLES FOR SCREWS In specifying holes for socket screws, observe the followi ng rules: 1. Holes A which engage the screw bodies are specified 1/ 64 inch larger than body diameter 2. Counter bored holes B are specified 1/ 32 inch larger than the diameter of the screw head

3. Counterbore depth C is the same as the height of the head of the screw 4. Countersink diameter D is made the same as the head diameter of the flat-head screw. In the illustration, view 1 shows the section through a hole for a socket cap screw; view 2 shows the hole for a socket button head screw, and view 3 the hole for a socket flat head screw.


178

SOCKET

CAP

16-15. MINIMUM THREAD ENGAGEMEI'-!1

SCREWS

Socket cap screws are the most frequently used fasteners for tools and dies and they should be specified whenever it is possible to employ them. A socket cap screw is provided with a he ad within which has been broached a he xagonal socket for driving. Threads of all socket screws in the size range normally used are held to a Class 3 fit, a very accurate fit having

This table specifies the minimum amount of thread engagement which should be applied for various materials. The values recommended for steel and cast iron should be memorized because they are employed so frequently.

2

~A 3 Fig. 16-1 4. Sectiona l views of holes for various socket screws.

precise tolerances. After machining they are heattreated; a hardening and tempering process is applied to produce a correct combination of toughness without bri ttleness. The final stage in their manufacture consists of careful inspection for uniformity and accuracy. Some differences may be noted in socket cap screws obtained from different manufacturers. Some have plain heads; othe rs are knurled for ease in starting screws by hand; some stamp the size on the head; others are provided wi th two sizes of heads, conventional, and ove rsi ze for severe applications. Socket screws are also available in stainless stee 1 for use under corrosive conditi ons. Nylock screws are socket provided screws with a projectin g nylon pe llet inserted per man en tly in the body. When the threads are engaged, the nylon is compressed and displaced providing a locking thrust to prevent loos ening under vibration.

THREAD ENGAGEMENT It is important that th read engagement for socket screws be applied correctly. If too little is specified, it is possible to strip the threads in the tapped hole. On the other hand, excessive thread engagement should be a voided because no greater strength is provided and it is difficult to tap deep holes. Also , the deeper a hole is t
Steel

I = 1 1/ 2 D

Cast Iron

I =2D

Magnesium

I = 2 1/4 D

Aluminum

I = 2 1/ 2 D

Fiber & Plastics

I =3D & UP

Fig. 16- 15. Table for determining minimum thread engagement for various materials.

FORMULAS FOR THREA D LENGTH Simple formu las establish thread lengths. Let L equal screw length, 1 equal thread length, D equal screw diameter. For Coarse-Thread Series (UN C) threads ; I equals either 20 plus V2 inch or V2 L whichever is greater. For Fine- Thread Series (UNF) threads I equals either 1V2 D plus Y2 inch or 3/ 8 L whichever is greater.

16·16. PROPORTIOI'IS OF SOCKET CAP SCREWS Socket cap screws are drawn to the following proportions : A = length of the screw; B = thread length; C = head height, D =the body diameter; (Note also th at that C = D); E = root diameter of the thread; F = thread chamfer, drawn 1/32 to 3/ 32 inch wide, depending on screw size; G = angle of chamfer, 45 degrees. When the block to be fastened is made of hardened tool steel, distance H should never be less than 1V2 D. For machine steel, it need only be thick enough for adequate strength. Length of thread engagement I is l lh 0 for steel, with a minimum of 1 D under certain conditions, and 2 D for cast iron and some non-ferrous metals. Depth of the tapped hole J is applied in increments of 1/16 inch at least, never in increments of 1/32 or 1/ 64 inch. Distance K between the end of the screw and the bottom of the thread , and between the bottom of the thread and the bottom of the tap drill hole, is normally made 1/ 8 inch . Bottoming taps have from 1 to lY2 imperfect threads, and this fact must be taken into consideration when drawing blind holes. The thread must extend at least 1V2 times the pitch of the thread


179

8

L

Fig. 16- 16. Proportions of socket cap screws.

past the end of the screw. Length L of the thread chamfer is made 1/16 inch. Chamfer M is 45 degrees. At the bottom of the tap drill hole are drawn two lines at angles of 30 degrees, dimension t>t. They represent the conical depression ;noduced by the end of the tap drill. For harden eci tool steel parts, distance 0 between the end of the tap drill hole and the lower surface of the block must be greater than 1 0 (one diameter of the

screw body). When this distance is less than 1 0, show the tap drill running completely through the part. If this is not done, it is possible for the thin, circular section of steel to crack in hardening and fall ou t as a rough-edged disk . The hole which a screw engages is tapped all the way through when distance P from the end of the screw to the lower surface of the block is 1 0 (one diameter of the screw), or less.


180

long screws, as at B. Sometimes it is desirable to fasten two details together through a third component. The screw head is reached for fastening through a hole which clears it, as at C.

16·17. APPLICATION OF SCREWS There are three methods of applying socket cap screws: 1. The most commonly used method is to counter bore the hole for the screw as at A. The screw head engages this counterbored hole and its top comes flush with the surface after assembly. 2. In a variation of the foregoing, the hole is not counterbored to full depth, and the head protrudes a certain amount as at B. This is employed for fastening thinner plates. 3. In the third method, the hole is simply drilled and the screw head is left to protrude, as at C. This would be used for thin parts and in covered places.

A

OTHER FASTEI'otERS Other types of fasteners commonly used in the design of tools and dies would include the following: Socket flat head screws Socket button head screws Socket set screws Socket lock screws Socket shoulder screws Dowels Rivets. Although these types of fasteners are not employed so frequently, the designer should understand the specialized conditions which require their use . Dowels are also treated in detail in the remainder of this section, as well as rivets as they apply to tools and dies. 16·19. SOCKET FLAT HEAD SCREWS Heads ofthese screws are machined to an 82 degree included angle, dimension A. They are employed for fastening thin plates which must present a flat, unbroken surface. Avoid their use when possible, because they cannot be tightened as securely as cap screws. Employ them only for flush applications when plates to be fastened are too thin for counterboring. For tool work, socket flat head screws are always specified in preference to the slotted type. To draw the side view, first look up the head diameter in a handbook or manufacturer's catalog, and

c

B

Fig. 16-17. Three methods of applying socket cap screws.

16-18. FASTENING PLATES When components such as plates are fastened to both sides of a block, tap the block aU the way through. Screws engage the block from both sides to hold the plates, as shown at A. When the center block is not too thick, it is permissible to hold three parts by threading one and fastening the three with relatively

A

8

c

Fig. 16-1 8. Different methods of fastenin g plates.


181

mark ends of head diameter to the specified dimension. Then the tapered lines of the head are drawn with the protractor set to an angle of 41 degrees from the s crew axis, dimension B.

Fig. 16-21. Appl ication of a socket se t screw.

Fig. 16·19.-Application of a socket flat head screw.

16-20. SOCKE T BU TTON HEAD SCRE WS These screws are employed for fas tening plates in applications where a raised head is not objectionable. They should be used when plates are too thin for counterboring for cap screws, and surfaces need not be flush, or flat. In the design of small and medium size dies, they fasten the stripper plate, back gage, and front spacer to the die block. Button head screws project only slightly above the surface. Their rounded contours prevent injuries to operators' hands.

16-22. POINT STYLES FOR SET SCREWS There are si x style s of se t s crew points. The designer must be able to specify the correct style of point for the spe cific application. 1. The flat point is th e most commonly used type for jigs, fixtu res, and dies . Flat-point set sc rews are employed as adj ustable stops, clamp screws, and to lock hardened shafts. 2. Cup-poi nt set screws are used to lock pulleys, collars, gears , and other parts on soft shafts. The sharp edges cut into the metal of the shaft to effect more or less permanen t positionin g. 3. Cone-point set screws may be employed for the same applications as cup-point screws. However , a much more positive lock is effected because the shaft is first spotted or drilled to engage the conical point of the screw.

2

3

4

5

6

Fig. 16·22. Six poi nt styles for set screws.

Fig. 16·20. Applic at ion of a socket button head screw.

16-21. SOCK ET SET SCREWS When first developed, socket set screws were called "safety" screws. They were employed to lock rotating machine parts to their shafts . They replaced screws with protruding heads which were dangerous because clothin g could become caught by the whirlin g projection. A socket set screw is threaded its entire length , and it is provided with an in ternal driving socket at one end .

4. Oval- point set screws are employed to lock parts which are to be adjusted frequently relative to each other. A groove is ordi na rily provided of the same gen· eral contour as the set sc rew point which bears against it. This groove may be machined lengthwise, angularly, or in any other direction to the shaft axis. 5. Half dog-point set screws are frequentl y employed to en gage slots milled longi tudinall y in shafts. They allow lengthwise movement, but prevent ro tation. The point also acts as a stop to limit travel. 6. Full dog-poin t set screws are employed for exactly the same purposes as half dog-point set screws. They are not appreciably more efficient and therefore are now seldon used, and they must be specially ordered.

16-23 . PUNCH-R ETAINING SET SCREWS This table faci li tates selection of the correc t set screw size after punch head diameter A has been established. It will help to eliminate errors because,


182

in every instance, tap drill size B is larger than head diameter A of the punch. This method provides quick removal and replacement of nicked or broken punches.

lock screw hole for re-setting to a new position. In the design of dies, lock screws are employed to lock punch-retaining set screws under crowded conditions .

16-25. SQUARE-HEAD SET SCREWS In die design, only one application remains for such screws. This is as actuator for the automatic stop. This right section view of a representative die

PUNCH HEAD TAP DRILL DIA. A DIA. B

3/16 1/4 5/16 3/8 1/ 2 5/ 8 3/4 7/8

#7 (.201) #F (.257) 5/ 16 27/ 64 17/ 32 21 / 32 49/ 64 7/8

TAP

1/ 4 5/ 16 3/ 8 1/ 2 5/ 8 3/ 4 7/81-

20 18 16 13 11 10 9 8

Fig. 16·23. Table for selecting top drill diameter and set screw th read size when punch head diameter is known.

16-24. SOCKET LOCK SCREWS Lock screws have the same dimensions as socket set screws, except that they are much shorter, and the hexagonal driving socket is broached clear through the screw. The length is one-half the diameter for most sizes. They are employed to lock set screws to prevent th eir loosening. A big advantage for some applications is that the lock screw need not be completely removed for resetting the set screw. It is simply backed up a turn or so and the set screw socket is reached through the

Fig. 16-24. Ap plication of a socket lock screw.

Fig. 16-25. Application of a square head set screw (A) for actual· ing the automat ic stop.

illustrates the manner in which a square head set screw , A, is applied to operate and automatic stop . A jam nut, B, locks the screw against rotation . Note that the hole for the set screw is tapped V
16-26. SHOULDER SCREWS Shoulder screws are used to provide pivots for rocking members of jigs and fixtures and to limi travel of components. A shoulder screw is provided wit h

Fig. 16-26. Application of o socket shoulder sc rew.

HOW TO APPLY FASTENER.S

183

a body ground to accurate size, a head with an internal driving socket, and, at the other end, a smaller threaded portion. The illustration shows a corner clamp employed to clamp square and rectangular workpieces against locating buttons for accurate positioning. The ccrner clamp pivots about a shoulder screw, A, which is threaded into the base.

16-27. STRIPPER BOLTS When shoulder screws are employed i n dies , they are called stripper bolts, bec ause they find their most common application in limiting travel of s pring strippers. This front section view of a blan king die shows an application of stripper bolts A, employed to retain a spring stripper and to limit i ts travel. Four or more s trip per bolts are used, but it is comm on practice to draw only one at one side in order to sh ow one of the springs at the other side of the view.

A

B Fig. 16·28. Applic ation of a tel esco ping s leeve pro vid es long travel of o stripper bo lt.

Fig. 16·27. Applicat ion of a stripper bolt (A) to li mi t tra vel of a spring st ripper.

16-28 . TELESCOPING SLEEVE When stripper plates or pressure pads require long travel, but stripper bolts cannot extend below the die set because the bolster plate of the press is not provided with a clearance hole , a telescopin g sleeve may be employed to increase the amount of travel. At A, the pressure pad is illustrated in raised pos ition. At B, it is shown at the bottom of the press stroke with the sleeve telescoped over the stripper bolt.

16-29. HOLES FOR STRIPPER BOLTS When specifying holes for stripper bolts, observe these rules: 1. Holes A which engage stripper bolt bodies are specified a slip fit, or sliding fit, by giving nominal diameter followed by the abbreviation S.F. Example: Y2 DR. & RM. THRU- S.F. 2. Counterbore diameter B is specified 1/ 32 inch larger than the diameter of the head of the screw.

Fig. 16·29. Hole foro strip per bolt.

16·30. SAFE STRENGTH OF SCREWS As a general rule, the strength of a socket screw is comparable to the strength of an ordinary screw of the next larger standard diameter. For example, a 5/ 1618 soc ket cap screw is about as strong as a 3/ 8-16 hexagon head cap screw. Many factors enter in to the determination of strength of screws. In designing, we are not concerned about the strength of a screw in its free state. Instead, we must know the amount of strength remaining in it after it has been tightened. A considerable proportion of the strength of a screw is expended in tightening. What is left is the effective load-carrying capacity. This table lists load ratings for socket cap screws, socket flat-head screws, and s ocket button -h ead screws. The table is based on a breaking stren gth of 180,000 pounds per square inch to which mos t s ocket screws are manufactured. Rea d the values di rectly in s electing

184


die fasteners intended to resist specific loads. These values will be found of particular importance in determining the sizes and number of screws required for fastening punches and stripper plates. SOCKET CAP SCREWS

SCREW SIZE

>-----H4

6 8 10 1/ 4 5/ 16 3/ 8 7/ 16 1/2 9/ 16 5/ 8 3/ 4 7/ 8 I

N.C ..

540 810 1,250 1,565 2,850 4, 620 6, 950 9,25 0 12,400 15 ,500 19,150 27, 500 38,500 48,500

N. F .

SOCKET FLAT HEAD SCREWS N.C.

N,F ,

465 585 700 910 1,080 1,315 1, 350 1,545 1,7 90 2,805 3,260 2,460 4,480 5,200 4,045 5,595 6,790 7,900 9,185 10, 400 8,215 14,000 10,975 12,375 17 ,200 21, 700 17,485 19,800 30,750 25,880 28,860 41,900 54,500

SOCKET BUTTON HEAD SCREWS N.C.

N.F.

1,010 1,260 2,300 3,785 5,595

1,060 1,445 2,625 4,190 6, 300

10,250

AFTER TIGHTENING: EFFECTIVE STRENGTH , IN POUNDS, TO RESIST LOAD .

16,350

Fig. 16· 30. Table of eff ective strengt hs of socket cap screws, sock et fla t head screw s and socket button head screws.

After the stripping force has been calculated, turn to the table and read values directly. When selecting stri pper bolts, choose values given for socket cap screws of the same diameter and threads per inch as the threaded portion of the stripper bolt.

16-31. DOWELS Dowels hold parts in perfect related alignment by abs orbing s ide pressures and lateral thrusts. Also, they faci litate quic k disassembly of components and reassembly in thei r exact forme r relationsh ip .

OVERSIZES Dowels are manufactured in two amounts of oversize : 1. Regular dowels, employed for all new jigs , fixtures, and dies are made 0. 0002 inch oversize to provide a secure press fit. 2. Overs ize dowels are made 0.001 inch oversize . They are used for repair work when dowel holes have been enlarged through repeated pressing of dowels in and out, an d when holes have been accidentally machined oversi ze.

SURFACE FINISH Manufac turers precision grind dowel surfaces to a diameter t olerance of plus and minus 0.0001 inch . Surface roughness is held to a finish of 4 to 6 microinches average, maximum. This extremely smooth finis h reduces the possibility of galling or seizing whe n dowels are driven in or out of their holes. A rust preventative coating is then applied.

16-32. DOWEL SHAPE Standard dowels are given a 5 degree taper at one end for easy starting when they are pressed in, as shown at A. A small radius is a pplied to the other corne r. However, to save time, they are drawn con ven tion ally by showin g a chamfer at each en d, as shown at B.

++--[1 - ·A

B Fig . 16· 32. Dowel shape in actuality (A) and as sho wn on a drawi _ (B). Fig. 16· 31. Typ ical appl ication of a dowel.

P resen t day dowels are precise tool comp onents , carefully designed and engineered. They are produced with exac ting acc uracy, both dimensionally and in their physi cal characteri stics. Dowels are made of a lloy steel, heat treated to produce an extremely hard exterior surface with a somewhat softer , but tough core to resist shear and spread, or mus hrooming, when they are driven in to tight holes . Surface ha rdness is Rockwell C 60 to 64 ; core hardness C 50 to 54 . Depth of the hard exteri or case extends from 10 to 20 thous andths of an inch depending on size , s maller s iz es havin g a thinner case . Do wels a re availab le in a range of sizes from 1/ 8 inch di amete r by 3/ 8 inch long, to 1 inch diameter by 6 inc hes in length .

STRENG TH Single s hear strength range s from 150,000 to 210,000 poun ds pe r s quare inch. To find the shear s trength of a dowe l, multiply the dowel area by the above values.

16-33. SHEA R STRENGTH OF DOWELS The s afe lo ad that dowels can resist in s he ar i_ determined by dividing the ultimate strength by thE area of th e dowe l. This table lists safe s hear s tren g s DOWEL DIA.

1/ 8 3/ 16 1/ 4 5/ 16 3/8 7/ 16

1/2 5/8 3/ 4 7/8 1

SAFE LOAD IN POUNDS

164 368 65 5 1,022 1,473 2,004 2,61 8 4,090 5,890 8,01 7 10,472

Fig . 16-33. Ta bl e of safe load s for a lloy stee l dowe ls in sin __ sh ear.


185

of dowels from 1/ 8 to 1 inch in diameter. Ultimate shear strength is taken at 190,000 PSI, and a safety factor of 12 has been applied. Therefore, these are safe loads for dowels in single shear under shock conditions as encountered in the design of dies. For· double shear applications, values should be doubled. The table lists stren gths of alloy dowels , and not of the less expensive cold-drawn steel dowels. Alloy dowels should always be used for dies because they are considerably stronger.

employed and the hole H is specified 1/32 inch larger than the diameter of the dowel for relief. This relief is applied to that portion of the hole not in actual contact with the dowel surface. Engagement length L is 1;6 to 2 0.

16-34. REAMING DOWEL HOLES When a hole is to be reamed for press fitting a dowel, it is first drilled with a reamer drill , then reamed. Reamer drills have the same nominal size as the corresponding reamers, but their diameters are actually smaller. For instance, a 5/ 16 inch reamer drill has a diameter of 0.307 inch and actual reamer size is 0.3125 inch, leaving 0.0055 inch of metal for the reamer to remove. The table lists sizes of commonly used reamer drills and their corresponding reamers. REAMER DRILL

REAMER

DIAMETER

DIAMETER

NOM INAL SIZE

DECIMAL SIZE

NOMINAL SIZE

DECIMAL SIZE

5/ 16 3/8 7/16 1/ 2

.307 ,366 .427 .489 .616 .734

5/ 16 3/ 8 7/ 16 1/ 2 5/ 8 3/4

.3125 .375 .4375 .500 .625 ,750

5/8 3/4

Fig. 16-34. Table of commonly used reamer dril ls and corresponding reamers.

16-35. PROPORTIONS OF DOWELS Conditions under which dowels are employed determine the type of application chosen. These are four:

1. Through dowels. In this application the hole is reamed all the way th rough the components, and dowels can be pressed out from either side. Dimension Ais two inches or less. Dowel engagement B is between 1;6 and 2 times diameter D 2. Semi-blind dowels. In this application the dowel hole is drilled and reamed from one side at least 1/ 8 inch deeper than dowel length. A smaller hole is drilled through the block and the dowel can be pr essed out from one side only. Dimension C of the knockout hole is made 1/2 D plus 1/ 64 inch, or one-half dowel diameter with clearance for a standard diameter hand punch for pressing out 3. Blind dowels. This dowel is applied in a blind hole, one not drilled and reamed completely through . The application should be avoided whenever possible . Blind dowels are more difficult to fit because of trapped air, and removal can be troublesome. Diameter E is made a press fit. Diameter F at the blind side should be a slip fit 4. Relieved dowels. When doweling blocks over two inches thick (dimension G), standard length dowels a re

Fig. 16-35. Four ways of applying dowe ls: through dowel (1); semi· bli nd dowel (2), bli nd dowel (3), re lieved dowel (4).

Normally, dowels are press fitted into both members. Holes are drilled and reamed after the jig, fixture, ot· die has been completely assembled, and often even after it has been tried out. However, when parts are subject to frequent disassembly , as for instance for sharpening, dowels are press fitted in one component and made a sliding fit in the other for ease of dis assembly.

16-36. DOWELS FOR MULTIPLE PARTS In precision tool design where clearances are held to extreme accuracy, good doweling methods must be employed. When more than two parts are to be doweled, the method shown at A may be used when plates are relatively thin. Dowel length is the same as the thick-

A

8

Fig. 16-36. Application of dowe ls fo r mu lti ple ports.


186

ness of the combined plates. For thicker plates and blocks, the method illustrated at B is preferred . Two dowels engage each dowel hole. The outer plates are thus doweled to the center block. It is common practice to made the length of a dowel four times its diame ter, when possible. For example, a 3/ 8 inch diameter do wel would be 1Y2 inches long.

16-37. DOWELING HARDENED PARTS There are three methods of doweling hardened toolsteel blocks . In the first, shown at A, holes are drilled and reamed before hardening. After hardening, they are either jig-ground or lapped for accurate engagement of dowels. In a second method B, soft plugs of machine steel are pressed into oversize holes in the hardened blocks. Holes for dowels are drilled and reamed through the soft plugs in a conventional manner. When doweling a machine steel block to a hardened too I steel block C, the hardened block only may be provided with a soft plug pressed into a large hole. Dowel location is transferred from the machine steel plate to the soft plug for accurate location and fit of dowe ls.

c

B

A Fig. 16· 37. Methods

of

doweling

hardened

B

c

Fig. 16·39 . One type of removable dowel for use in blind hole applications.

16-40. MEREDITH DOWELS An ingenious removable dowel for use in blind holes is the Meredith dowel recently paten ted. This do wel Ais provided with an axial hole tapped the entire length of the dowel. Threaded into the hole is a long socket set screw B. In section view C, the dowel is shown pressed in to a blind hole. For removal , the set screw is turned as shown in view D and this jacks the dowel upward out of the hole.

t oo l·stee l blocks.

16-38. DOWEL DIAMETER For jigs, fixtures, and gages, always make dowel diameters one size smaller than corresponding screw diameters. For dies, dowels are made the same diameter as the screws because of the high speed and shock conditions present in operation. This table lists correct dowel sizes for screws ranging from number 8 to %inch in diameter. SCREW DIAMETER

#8 # 10

1/ 4 5/ 16 3/ 8 7/ 16

l/2 5/ 8 3/ 4

DOWEL DIAMETER TOOLS

DIES

1/8 1/8 3/ 16 1/ 4 5/16 3/8 7/16 1/ 2 5/ 8

1/ 8 3/ 16 1/4 5/ 16 3/8

7/16 1/ 2 5/ 8 3/4

Fig. 16·38. Screw diameters and corresponding dowel diameters as appl ied to too ls and die s.

16-39. RICHARD BROTHERS' DOWELS l
c

0

Fig. 16·40. Another typ e of removable dowel for use in bli nd ho le applica tions.

16-41. RIVETS l
16-42. RIVET APPLICA TIOHS Riveting is not often employed for fastening di e parts. There are two exceptions:


187

1. The knockout rod is usually turned down at its end, pressed into the knockout plate , and the en d is then peened or riveted over, as shown at A 2. In ano ther application, the strip support is often riveted to the back gage, as shown at B.

dieiDaker, so more material can be allowed than for machine riveting. Flat-head riveting is done by peening with the round end of a ballpeen hammer. After riveting, any excess metal is removed by machining to provide a fl at surface.

8

A

c Fig. 16·41. Two types of rivets commonly used in tools and dies.

GRIP

II

A

II

1/ 4 3/ 8 1/ 2 5/ 8 3/ 4 7/ 8 I I 1/8 1 1/ 4 1 3/ 8 1 1/ 2 1 5/8 1 3/ 4 1 7/ 8 2

II

RIVET DIAMETERS 1/ 8 5/ 8 3/ 4 7/ 8 1 1 1/ 8 I 1/ 4 1 3/ 8 11 / 2 I 5/ 8 1 3/ 4 1 7/8 2 2 1/ 8 2 1/ 4 2 3/ 8

3/ 16 3/ 4 7/ 8 1 1 1/ 8 1 1/ 4 1 3/ 8 I 1/ 2 I 5/ 8 I 3/ 4 1 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2

1/ 4 7/ 8 I I 1/ 8 I 1/4 1 3/ 8 1 1/ 2 1 5/ 8 I 3/ 4 I 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2 2 5/ 8

3/ 8 1 I 1/8 I 1/ 4 I 3/ 8 1 1/ 2 1 5/ 8 I 3/ 4 I 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2 2 5/ 8 2 3/ 4

1/ 2 1 1 1 1 I 1 1 2 2 2 2 2 2 2 3

3/ 16 5/ 16 7/ 16 9/ 16 11/ I6 13/ 16 15/ I6 1/ 16 3/ I6 3/ 8 1/ 2 5/ 8 3/ 4 7/ 8 1/ 16

5/ 8 I 3/ 8 I 1/ 2 1 5/ 8 1 3/ 4 1 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2 2 11 / 16 2 13/ 16 3 3 1/8 3 1/ 4

3/ 4

II

1 1/ 2 I 5/ 8 1 3/ 4 1 7/ 8 2 1/ 16 r 2 3/ 16 t"l 2 3/ 8 >-l 2 I / 2 ::c 2 5/ 8 2 3/ 4 (D 2 15/ I6 3 1/ 16 3 1/ 4 3 3/ 8 3 1/ 2

6

-...,

I _.J

A

8

Fig. 16·42. Two instances where riveting is used to fasten die parts.

16-43. RIVET PROJECTION In applications which require riveting, an important consideration is the amount that the rivet end must project for upsetting or riveting. If thi s amount is insufficient, the riveted joint will be weak. If too long, excessive pressure or peening will be required and an unsightly joint wi ll be formed. These tables list correct lengths of projections for rivets from 1/8 to 3/ 4 inch in diameter. Nate that when a tool component is turned down for riveting, as for instance a knockout rod, the same amount of projection would be applied, determined by its diameter. Riveting of die components is done wi th a hand rivet set and sledge. The work is performed by a ski lled

RIVET DIAMETERS

GRIP

A

~ 3/ 8 1/ 2 5/ 8 3/ 4 7/ 8

I I 1/ 8 I 1/ 4 1 3/ 8 1 1/ 2 1 5/ 8 I 3/ 4 I 7/ 8 2

1/ 8 3/ 8 1/ 2 5/ 8 3/ 4 7/ 8 1 11/ 8 11 / 4 I 3/ 8 I 1/2 1 5/ 8 1 3/ 4 1 7/ 8 2 2 1/ 8

3/ 16 1/ 2 5/ 8 3/ 4 7/ 8 1 1 1/ 8 I 1/ 4 I 3/ 8 I 1/ 2 I 5/ 8 1 3/ 4 I 7/ 8 2 2 1/ 8 2 1/ 4

1/ 4 5/ 8 3/ 4 7/ 8 1 1 1/ 8 1 1/ 4 I 3/ 8 I 1/ 2 I 5/ 8 I 3/ 4 I 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8

3/ 8 3/ 4 7/ 8 1 I 1/ 8 1 1/ 4 1 3/ 8 I 1/ 2 I 5/ 8 l 3/ 4 1 7/ 8 2 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2

1/ 2

5/ 8

3/ 4

13/ 16 15/ 16 1 1/ 16 1 3/ 16 1 5/ 16 1 7/ 16 I 9/ 16 1 11 / 16 I 13/ 16 1-15/ 16 2 1/ 8 2 1/ 4 2 3/ 8 2 1/ 2 2 11/16

7/ 8

7/ 8 1 I 1/8 1 1/ 4 1 3/ 8 1 9/ 16 I 3/ 4 1 7/ 8 2 2 1/ 8 2 5/ 16 2 7/ 16 2 5/ 8 2 3/4 2 7/ 8

1 1 1/ 8 1 1/ 4 1 3/ 8 1 1/ 2 I 5/ 8 1 3/ 4 I 7/ 8 2 2 3/ 16 2 5/ 16 2 1/ 2 2 5/ 8 2 3/ 4

=

r

t"l

z

C'l

>-l

::c

(D

Fig. 16·43. Tabl es of lengths of projections necessary for good round head and flat head riveting.

Section 17

HOW TO SELECT A DIE SET Afte r all die details have been designed, a die set of the proper size and style is selected from a manufacturer's catalog and drawn in position. Between five and ten per cent of total desi gn time i s spent in selecting and drawing the views of the die set. This allowance may be increased considerably if the designe r does not thorough ly understand the principles underlying die set selection and representation. Die sets are manufactured in a bewi ldering variety of sizes and shapes and it is the purpose of this section to acquaint you with the various styles as well as to indicate proper methods of selection and placement. Advantages realized when die components are retained i n a properly selected die set are:

be specified only for dies which perform bending, forming, or other non-cutting operations.

MATER IALS Selection of the material from which the die se is to be made will depend upon strength requirements. There are three choices: 1. Semi-steel 2. All steel 3. Combination - i n which the punch holder is semi-steel and the die holder is all steel.

SEMI-STEEL In manufacturers' catalogs the material of the die set is listed as either semi-steel or steel. Semi-stee_ contains only about 7 per cent of steel in its con:posi tion and is considered to be cast iron. Semi-stee: die sets are cast to shape and then machined. So e manufacturers may cast punch holders and die holde~s of Meehanite which may be considered a highgrade cast iron.

1. Members are kept in proper alignment during the cutting process, even though some looseness may exist in the press ram. Thus, uniform clearances are maintained around cutting edges for producing blanks free of burrs 2. Die life is increased 3, Dies can be installed in the press in a minimum amount of time because they are self-contained units 4. Storage is facilitated, There is no possibility of lo ss of loose parts 5. Properly designed dies can be sharpened without removal of cutting members. Standard die sets range from 3 by 3 inc hes to 45 by 60 inches, Die hol der and punch holder t hicknesses range fro m 1 to 3Yi inches, by 'luarter i nches.

STEEL DIE SETS When a large hole is to be machined through he die set for blank removal, it is considered good pract ice to specify a steel die holder. This prevents fract u~e of the die holder if placed over a large hole in h., bolster plate, which is done occasionally even in ·.e best press shops. It happens too frequently that a cas:iron die holder is actually broken in two because : t he weakening effect of a large hole in conjunc ·awith insuffi cient support under pressure. Steel die sets are thorough ly stress-relieved · ma nufacturers before final machining or grind i s Stress relieving removes any stresses introduced :the material in rolling at the mill and other stress...<>S added du ring rough machi ning. If s uch residual stres e5 are not removed, they are gradually released with co-sequent distortion and dimensional change, which c-ruin a precision die. Obviously, it behooves the designer not to i nc :porate anythi ng in the design which can introd = stresses in the die set while the die is being bu· · Welding anything to a die set must be avoided. Ro smachining of deep pocket s s houl d be done by the set manufacturer before the stress relievi ng operatic and a print showing necessary machining opera io- :

ACCURACY Die sets are manufactured to two standards of accuracy: precision and commercial. P unch-holder and dieholder tolerances are the same for both. The difference between t hem occ urs in the closeness of fit between bush ings an d guide posts. For precision sets, tolerances between bushing s and guide posts are maintained from 0.0002 to a maxim um of 0.0004 inch. This tolerance assures extremely accurate alig nment between punches and corresponding holes in die blocks. For this reason, precision die sets should be specified for all dies which perform cutting operations. Commercial die sets are given more liberal clearances between bushings and guide posts. These range from 0.0004 to 0.0009 inch. Commerci al die sets should 188

189

HOW TO SELECT A DIE SET

should accompany the purchase order. To illustrate the importance of stress relieving in the man ufacture of die sets with deep milled pockets and through holes, here is a representative order of operations actually employed for a larger die holder 1. Flame-cut holes 2. Stress relieve 3. Surface grind 4. Rough machine pockets 5. Stress relieve 6. Surface grind 7. Finish-machine.

- - A

11 m

B

SELECTING TH E Dl E SET Ten elements of die-set information must be 9ecided before a die set can be ordered: 1. Make or manufacturer 2. Type 3. Size 4. Material 5. Thickness of die holder 6. Thickness of punch holder 7. Type and l engths of bushings 8. Lengths of guide posts 9. Shank diameter 10. Grade of precision. In selecting a die set from a catalog, first consider I the dimensions from front to posts and from side to side. This is the die-set area or usable space, to which die details can be fastened. Next in importance is the thickness of the die holder and of the punch holder,

-0

Fig. 17-1. Components that make up a die set.

A

A

17·1. DIE SET COMPONEN TS These are: A. Punch holder B. Guide bushings C. Guide posts D. Die holder. When the die set is assembled, the lower ends of the guide posts are pressed securely into the die holder and the turned down portions of the guide bushings are pressed into the punch holder. The bushings engage the guide posts with a close sliding fit to provide accurate alignment. The illustration typifies small and medium-size die sets made of both cast iron and steel, although different manufacturers may incorporate slight variations.

17·2. PUNCH HOLDERS The upper working member of the die set is called the punch holder. The name is easy to remembe r be cause of its relationship with the punches, which are no rmally applied above the strip and fastened to the underside of the punch holder, Surfaces A are finished. They are employed by the die maker for squaring and locating punch components of the die. Surfaces B are also finished surfaces. The upper one bears against the undersi de of the press ram. Punch components are fastened to the lower finished surface.

Fig. 17·2. A typic al punch holder,

17·3. INVERTING THE PUNCH HOLDER On a die drawing the punch holder is show n inverted or turned over, At the upper portion of the illustration the die hol der is shown at the l eft and the punch holder at the right, exactly as they appear on the drawing. At the bottom is shown how the punch holder is removed from the guide posts and inverted to an upside down position for drawing.


190

At the upper right view the punch shank is re presented by a dotted circle and the bushings by concentric solid circles. The pun ch holder is drawn inverted in this manner because this is the position in which it is placed on the die maker's bench for assembly of punches. Also, punches can be drawn with solid object lines, which makes the drawing easier to draw a nd read.

the punch shank and the fillet B at the bottom where it joins the punch holder are given a 1/ 8 inch radius on the drawing. Larger die sets are not ord inarily provided with a punch s hank, or the shank is employed only for centerin g the die and not for drivin g. Instead, such die s ets are clamped or bolt ed to the underside of the ram because of the considerable wei ght of large punch holders and punch members, The relatively small punch shank would not be a safe method of driving. To supplement the holding power of the shank, socket cap screws are often inserted upward through the punc h holder to en gage hol es tapped in the pres s ram. Where this practice is followed, the designer specifies and dime nsio ns the mounting holes to matc h the hole pattern in the ram, and he must make certai n that they clear punch components. Dimensions for mounting holes are ordinaril y taken from a company standards book,

17-5. DIE HOLDERS

Fig. 17·3. How a punch ho lder is inverted and shown on a drawing.

17-4. PUNCH SHANK The punch shank projects above the punch holder and it aligns the center of the die with certerline of the press, In operation, the shank is clamped securely in the press ram and it drives the punch portion of the die, raising and lo wering it for perfonning cutting and other operations. For semi-steel die sets, the punch shank is cast integrally with the body of the punch holder and it is then machined, For steel die sets, it is electrically welded to the punch holder and then machined. Punch shanks may also be ordered separately. These are turned down at one end and threaded for en gagement in a large tapped hole in the punch holder. Punch-shank diameter depends upon the press selected. It is usually determined from a company standards book and it should be checked carefully for accuracy . After the diameter is known, the length can be found listed in a die-set catalog. The round A at the top of

The die holder is the lower worki ng member of the die set. Its shape corresponds with that of the punc holder except that it is provided with clamping flanges A having slots for bolting the die holder to the bolste r plate of the press. Machined surfaces B are employed for squaring an· locating die components. Surfaces C are also finished . The lower one rests on the bolster pl ate, and the die block and other components are fastened on the uppe: surface. Usually, the die hol der is made thicker than the punch holder to compensate for the weakening effect o: slug and blank holes which must be machined throug:: it. Common proportions for s mall and medium-siz e dies are: Punch holder thickness - 11;4 inches Die holder thickness -1¥2 inches .

8

8

,----- A

-----8

Fig. 17·4. Punch shank pro jecting above punch ho lder is given a 1/ 8 inch radius at (A) and (B).

'c

Fig. 17·5. Typical die holder with clamping flanges (A) and moe surfaces (B) and (C).

i-~

191


17-6. GUIDE POSTS

17-7. REMOVABLE GUIDE POSTS

Guide posts are precision-ground pins which are press-fitted into accurately bored holes in the die ho lder. They engage guide bushings to align punch and die components with a high degree of closeness and accuracy. There are six types: 1. Small guide posts are usually hardened and centerless ground, particularly for the commercial die-set grades 2. Larger diameter posts a re ground between centers after hardening 3. Posts may be relieved at what will be the die set surface, This relief is usually applied to precision posts 4. A non-sticking post end may be incorporated, This provides for quick and easy assembly and disassembly 5. Shoulder guide posts are employed in conjunction with shoulder guide-post bushings. The l arge shoulder is the same diameter as the press-fit portion of the guide bushings. In the manufacture of special die sets, the punch holder and die holder are clamped together and holes are bored through both for engagement of bushings and guide posts 6. Removable guide posts can be easily removed from the die for sharpening. They are employed for large dies and for dies having more than two posts. Guide posts for precision die sets are hard -chromium plated to provide a high degree of resis tance to wear. Also, the addition of a chromium surface reduces fri ction by more than fifty per-cent.

Often guide posts must be removed for die sharpen· ing, especially in large dies and in dies having more than two posts of the back-post style. There are three types: 1. Danly and Standard Die Set removable guide· posts have an axial hole machined through them and tapered at one end to engage a taper pin A. The post end is slotted. By driving the taper pin , the post is expanded against the walls of the hole in the die holder. To remove the post, a long rod called a drift is inserted from the top and the tape r pin is pressed out

8 A

c

F

2

3

Fig. 17·7. Three types of removab le gu ide posts .

2. In Producto removable guide posts, the taper pin B is advanced for locking the post by means of a socket cap screw C 3. Union removab le posts are provided with a taper at the lower end to engage a s leeve for bushing D, which is pressed in to the die holder. A socket cap screw E engages a retaining cap F to clamp the post to the bushing. Removal of the socket cap screw a llows the post to be lifted up and removed.

17-8. t--IOt--1-STICKit--IG GUIDE POSTS 2

3

4

5

6

Fig. 17·6. Six types of guide posts.

For secondary-operation dies, guide posts should have sufficien t length so that they never leave their bushin gs in operation. This is a safety feature to prevent possible crushing of fingers accidentally introduced between posts and bushings as the die is operated. Guide posts are specified at least ~ inch shorter than the shut height of the die as listed on the drawing, (the shu t height bein g the distance from the bottom su rface of the die hol der to the top surface of the punch holder, excluding the shank, and measured when the punch holder is in the lowest working position). This provides a grinding allowance to assure that the top of the posts will not strike the underside of the press ram when the upper die is lowered as punches are sharpened.

Sticking or jamming in initial stages of engagement of punch holder and die holder has long been a problem because of the close fits maintained. Sticking occurs WJtil the bushings have engaged the posts sufficiently for complete alignment. Dies must be assembled and disassembled a great number of times in their manufacture, tryout , and in sharpening. Shown at 1 is the McVey post originated by C.H. McVey and manufactured by the Standard Die Set Co. of Providence, R.I. The following are features of this post: A. A ground taper guides the bushing over the post B. A narrow land of the same diameter as the post centers the bushing. The land is narrow enough to allow rocking of the bushing over it C. This clearance area represents the sticking range. Because metal has been removed, sticking cannot occur D. This is a ground lead which guides the hushing


192

to engagement with the full diameter of the post. Shown at 2 is the Producto guide post . It has a radius at the leading end and this aligns the bushing.

the die holder. Most bushings are made of tool steel although they are also available in bronze. There are two types: 1. Plain bushings are simple sleeves pressed into the punch holder 2. Shoulder bushings are turned down at on.e en d and they are pressed in to the punch holder against the shoulder thus formed. They are recommended for al dies which perform cutting operations, Lengths of guide bush ings vary, dependi ng upo the manufacturer. In ge neral, we may recogniz e two different lengths for plain bushings- regular and long. Shoulder bushings are furnished in three 1engths regular, long, and extra long, The length selected w· : depend upon the accuracy requirements of the die. The longer the bushing, the more accurate will be the al i gnment of punch and die members. This is particularl _important in cutting operations, especially for thi:: stock when clearances between cutting edges are smaL

2 Fig. 17·8. Two typ es of comme rcially-available guide pas ts deve loped to overcome st icking or jamming in initi al stages of engagement of punch and die holders.

17-9. OFFS ET POST ENOS In another method of assembly employed by Danly Machine Specialties, Inc., one of the guide posts is made longer than the other. The punc h holder engages the long post first and it is thus aligned before engagement of the other post occu rs. Dimension A is usually made Y:z inch. A

L_

I

~

2 Fig. 17-10. Two common type s of guide bushings.

Posts and bushings are assembled by shrink fit ·-:_ into holes bored in the punch holder and die holde:. The post s and bushings are subjected to deep freez · thereby reducing their diameters. They are then in ser.e: in the punch holder and die holder and upon war mi-~ to roo m temperature, they expand to provide a i~ -: fit between componets. Each guide bushing is provided with a fitti ng :-:lubrication. Helical grooves are machined in ins:::~ surfaces for retention and distribution of the lubri c~ ·

17-11 . SELF OILING GUIDE BUSHINGS

I

I

l

I

Fig. 17·9. Use of guide posts of diffe ren t lengths facilitates engage· ment of punch and die ho lde rs.

17-10. GUIDE BUSHINGS Accurately ground sleeves, or guide bushings, engage guide posts for aligning the punch holder wi th

Richard Brothers' guide bushings are made of por _, powdered alloy steel. Internal pockets are cored in : ·::walls, and these are filled with oil at manufacture, use, the oil meters through the porous walls by cap!: ary action. Stored lubrication is sufficient for the .::~ of the bushing,

17-12. DEMOUNTABLE GUIDE BUSHINGS These are shoulder bushings provided with cla:::?: that engage an annular groove machined in the bus'· : wall or shoulder. Socket cap screws are threa __ : into the punch holder to effect clamping. The t ::-:down portion of the bushing is not a press fit into ·- .


193

punch holder, Instead, it is ground to an accurate sliding fit for ease in disassembly. These bushings are available in bot h steel or bronze, and they are provided wit h either two clamps A or three Clamps B, depending on size. Demountable guide bushings are specified for long runs, when it is anticipated that bushings and posts will require replacement.

are turned down for location in holes in the die set and they are fastened with socket cap screws for easy replacement. There are three types of boss bushings: L Flange mounted - the greater portion of the bearing surface is wi thin the die set 2. Demountable - employed as bearings and also as guide-post supports 3. Long bearing - these have a bearing surface extending below the mounting flange and supported by ribs,

17-14. BALL-BEARING DIE SETS Some die sets are provided with ball bearings instead of guide bushings, Guide posts are pressed into the punch holder and they engage linear ball bearings A, which in turn are guided in hardened sleeves B pressed into the die holder, The bearings are preloaded to remove looseness or side play, Lubrication is by cup grease applied at set up and this is usually sufficient for the entire run. Ball bearings take up mo re room than conventional guiding methods and they reduce die s pace a small extent. Fig. 17-11. A commercia lly-available self oiling guide bushing made of porous powdered alloy ste el.

B

A

Fig. 17· 12. Demountable guide bushings ore used far lon g runs.

17-13. BOSS BUSHINGS Demountable bosses may be employed as guide bushings in large die sets. They are used for heavyduty work when long runs are expected, The bosses

~ ~ I I I I

!

I I

I

I I

I

I

Fig. 17·14. Set up in which ball bearings are used instead of a guide bushing.

17-15. DIRECTION OF FEED Direction offeed of the strip will influence selection of the die set, Strip may be fed through a press in any of three directions: 1. Front to back, This method may be employed for long runs when strip is fed automatically

I I

I I I I I

I I I

~

I 2

3

Fig. 17·13. Three types of demountable bos s bushings for heavy· duty work in long runs.

2

D

c:;> 0

3

Fig . 17- 15. Three directions in which the strip may be fed through the press.


194

2. Right to left, This is the most commonly used feeding direction. It is always employed when the strip is advanced by ha nd 3. Left to right, This directio n is occasionally used when the strip is fed automatically. Feed direction must always be ascertained before design of a die is started because it will affect the se1uence of o perations and location of stops.

17- 16. POST ARRANGEMENT Gui de posts may be posit ioned in any one of six ways: A. T wo posts are applied at the back of the die set. This is the most commonly used two-post arrangement B. Posts are applied at the sides for feeding strip from front to back. C. The posts are positioned diagonally, and at 0 fou r posts are used. The foregoing are standard post a rrangements as listed in die-set catalogs. Wh en rect angul a r steel die sets are ordered, any post arrangement may be supplied by t he die set manufacturer. For feeding strips sideways in long runs, so me desig ners prefer posts applied at the front a nd at the back as shown at E. Othe rs specify th ree posts for stability as shown at F.

STAN DARD

0

0 0

8

A 0

0

0

0

0

0

0

c

0 SPECIAL

0

0

0

0

0

E

F

Fi g. 17· 16. Six woys of arranging guide pasts in a die se t.

2. Shut height of die. Make certain that the shu hei ght dimension is well within the available die space witho ut the ram adjustment being taken up to its li mit. In this connection, make certain that gri ndin g clearance has been taken into consideration. 3. Distance from the center of the shank to the back of the die. Make certain t hat this dimension is a least \4 inch less than the distance fro m the center o the ram to the frame of the press, The make and mode~ nu mb er of t he p ress are marked on the route sheet, and specification s can be found in the manufactur er's catalog or in the company standards book,

2

3

Fig. 17 ·17. Terms app1 ied to presses: die space, (A); shut he ig-· (B); and height of shortest die (C) that press will accommo a·e

Look first for the "Die Space. " This is usuaL: _ specified as the distance from the bed of the pres s · the underside of the ram with the stroke down and :c.= adjustment up, dimension A. Next look for the thickness of the bolster pi a e. This must be subtracted from the die space to give-=.~ shut height from the top of the bolster plate, dimen Sl ~ B. This is the he ight of the tallest die which will :.· into the press. Howeve r, some manufacturers give :::-:= die space directl y as the distance fro m the top of : :o bo lster plate to the underside of the press ram , a::: cauti on should be exercised . Next, it will be necessary to determine the shor e die which th e press will accommodate. Look up -- = dimens ion for "Adjustment of Slide," The ram o: : . press is usually provided with an adjustment to ace -modate a range of die heights. Subtract the dimens. given for adjustment of slide from the shut heig;· This will be the height of the shortest die which --., press will accommodate, C. However, a die shut he \4 i nch higher must be used to allo w for loweri ng upper die as punches are sharpened from time to

17-17. PRES S DATA fter a di e has been tentativel y desi gned or rou ghed ou t, the next step is to consid e r the speci ficati ons of t he press in which it is to operate. This should be done before t he die set is selected because the available space may infl uence die-set size and type. It i s very import ant that a die fit the press for which it was designed, and it is the de signer's respo nsibility to ascertain that there will be no interferences, The three most important considerations in determining the dimensions of a die set are: 1. Punch sha nk diameter. Check the press data sheet carefully to make sure that the recess in the press ra m will accommodate the punch shank sel ected.

17-1 8. SPECIFICA liONS So that your understanding will be comple e every respect, I have included a representative s __ ifications page from a press catalog. Study those S?=":ifications which apply in the selection of a die set - ~ actually look up the dimensions as you proceec review the example to follow. Assume that a die is to be designed for use Federal press o. 4. The manufacturer's catalo g ::: the "Die Space" C as 9\4 inches, and "Bolster P -= Thickness" B as 1% inches. Subtracting 1% fro .. -: gives the maximum shut height 7Y2 inches. "Adj ustment of Slide" is listed as 2¥2 inch es. -

5:;:

IONS

SPEC

a c:J.l

~

tr.J 0 ...::l ~

g tr.J Federal OBI Press No.

Tonnage, capacity near botrom of stroke . .. SLIDE, standard stroke ...... , .. , ..... . .... . maximum stroke . . . . . . . . . . . . . . . . . . . . . . . .

adjustment of slide . ..... .. .......... . round punch sha nk hole {sq . hole optiona l) ... A

•

c D

• p

0 H

0

1

2

7 1'4 3 1 y,

15 1 Yz 4 1 Yz P At. 5 x4%

20 2

1

face a rea F. to B., R. to l. (f langes availab le) BOLSTER PLATE area F. to B., R. to l. . ... ' . thickness . ... ......... . . .... . ..... ... . DIE SPACE, bed to slide, stroke down adj. up ..

3~ox3 Ye

bolster plate to slide, stroke down adj. up .. . additiona l shut height w bed extension .. . BED depth of throat, rom cente r to frame . . ' . Std. opening in bed F. to B., R. to l. . .. ..

4'.4 1 to 4

Std. round opening . . . . . . ........ .. ... .. Std. ope ning through bock ...... .. ....... distance bed to gib s . ...... . . . . . . . . reclines from uprignl ... .. ... .... •

•••

0

••

C RANKSHAFT, dia . at ma in bearings .. .. • .. .. diameter at crank bearing . . . . . . . . . . ...

FLOO R SPACE overall F. to B., R. to l. .... legs only, F. to B., R. to L. .. , ........ •. ... height from floor to b ed ... . ..... . •. heigh t from floor to shaft center .. .. . . . .... height from floor to top of wheel ..... .. . .

6

X

9 3/.i 1

5*

31fz 3x5 . .... . .. 5'.4 7 40 °

8

15 1'4 71fl X

6\4 1 to 5 41fz 4x6

5 7Yz 9 40°

Jl/a 2:1,4 24 X 23 24 X 23 36 54

2'11• 2'11· 28 "26 27 X 21 31

62

64

580 655

1300 1400

75

180 150

54

33

3lf2

4

44

5

55

6

27

27

35

43

21f2 6 2 1 •;,.

21f2 6 2

3 8

3 8

43 6 10

56 4

56 4 12

60 4

1•11· 7Ye ){ 18 16 X 32 ]3,4

2Yz 1011,

2Yz l"At.

2Y> 2Yz

8 3.4 x 71fz 14 3_4 X 27

8* x 7 1fz 14 3/.i X 27

2Yz 2 1f2 11% X 12

]3,4

9Yz

9\4

1* 9'4

7'.4 1 to 6 83,4

7Y>

7Y>

1 to 6

1 to 6

8

7

7

8 7 ){ 12

3

5 1 Yz

p ;,, 5Y, ){ 5 10 x 17Yz 1\4 7* 61f2 I to 10

5Y> 5x7 7 BYz 1 0 '.4 40°

7l4x5Vi 12".4x211f2 1'.4 8* 7 1 to 12 7'.4 5 X 11 8 103,4 11 y, 40 °

2 '11• 2'11• 34 X 30

2* 3 42 ){ 35

32

38

X

21

c:J.l

X

29

32 59 70

33 63 76

1750

2800 2900 450 125 27Yz x 4 2-1200

X

21

12 10

X

. . ..... . 20Yz 14

40° 2lf.. 3

10

X

21

....' ' . . 21

12* 40°

12* 40 °

171f2 30°

3'.4

31fl 3".4 45 X 41

3Y> 3:1,4

57

X

40

48

X

3300 3450 450 125

4300 4450 700 120

27Y2 X 4 2 - 1200

32 X 5 3 - 1200

32 "5 3-1200

X

7

121fz

77

35 39 32 62 X

8 1 to 10 11 y,

12Y>

3* 45 X 41 40 X 34 32 67 83

45 40

2Yl 2Yz Blfz x 24 21 X 33 2 10

34 32 67 X

46 41

83

32 73 91

4500

7400

4650 720

7650 820 90 36 X 5'/.t 5 -900

8 2Yz 2 Yz 10x8 3.4 18Y>x291fz 2\4 1 0 '.4 8 1 Ia 6 10

8" 141f2 11 * 13Yz 15 '.4 30° 4 4% 50 X 48 48 X 36 32 72 92

11 Ya x 24 28 X 36 2 3,4 15 1 2 v.. I to 21 15 or 17 10 X 22 . .. .. . .. 22 or 26 21 y, 36° 4 4% 59 X 49 57

X 48 34 81 98

tr.J ...::l

6

251fz x 33 2* 13 10V.. 1 to 6

13 Yz 14 X 18 16 16 18 Y> 36° 4'11• 4% 60 X 58 57){ 40 33 81 102

FLYWHEEL TYPE PRESS

Weight, approximate .... . , .............. . Shippi ng weight, approximate ....• .. . . . . . . Fly whe el-weight . . .. ' .. . . . . . . . . . . speed (strokes per min.) . . . . . . . . . . . ..... . d iameter x width . ... _ . . . . . . , .

MOTOR H.P. and •peed . . .........

~

.....

175 16x21j,

.....

1f2·1 200

201fs x 3'.4 1-1200

1850 225 150 22Ya x 3Y, 1 Y>·1200

Fig. 17·18. Representativ e specifications page from a press catalog.

120

6700 6950 1000 90 36 'J. X 6 5-900

10500 10900 1000 90 36 ',4 X 6 5-900

11000 11400 1150

75 42Y> x 6 5-900

Federal Pr ess C o.

.....
196

HOW TO SEL ECT A DIE SET

tracting 2lh from 7lh gives a m1mmum shut height of 5 inches. Therefore, this press will accommodate dies ranging from 5 inches to 7lh inches high. However, a die with a 5 inch shut height, the minimum dimension, would not operate very long. After sharpening, the members would not come together because the press adjustment would be all taken up. Any die designed for this press should have a shut height of at least SY-t inches, thus allowing Y-t inch of material for sharpening. In effect then , the shut height of the die to be designed should be between 5V-t and 7% inches. Next, it will be necessary to look up dimensions for the recess in the slide for the punch shank. For a No. 4 Federal press, this is listed as 1 9/ 16 inch diameter. Punch shank diameter must be 1 9/ 16 also. Still another dimension to be taken into consideration is the stroke of the press. This is particularly important for bending, forming, and drawing dies. Should the stroke be too short, it might be impossible to place the part into the die or to remove the stampings from it. The stroke for a No. 4 press is listed as 3 inches, and it is called "Slide, standard stroke," One entry in the press catalog may be puzzling. This is "Maximum stroke of ram," or "Slide, maximum stroke," and the dimension is a! ways greater than the dimension for "Standard stroke of ram." For a No. 4 Federal press, it is given as 8 inches. This entire entry can be disregarded. It lists the maximum stroke for which the press can be built and the press can be modified to exert any stroke within this range. However, if a press. is built with a stroke other than standard, it will have a special number. Another dimension to be considered is the "Depth of Throat," E. This is the distance from the center of the press back to the frame. Since the punch shank is located at the center of the press, the distance from its center to the back of a die set must be less than the listed dimension. For the press under consideration, depth of throat is given as 8 inches. The corresponding dimension for the die set should be at least V-t inch shorter.

17-19 . ESTABLISHING THE DIE-SET CENTER Ten design steps are necessary in selecting and applying the views of a die set for a specific die design. Consider the following sequence carefully, because it provides a proper working method: 1. Determine the diameter of the punch shank. Punch s hank data is usually found in a company standards book or manufacturer's catalog, although occasionally it may be necessary to get it directly from the press room. On an appropriate sheet of paper, draw a circle of the required punch-shank diameter 2. On the upper left plan view of the die, draw vertical and horizontal centerlines. Their intersection represents the ideal center of the die; the one we should prefer to use if possible. For most dies, the ideal center would be the center of the die block, measured from side to side and from front to back. 3. Transferring measurements, draw corresponding centerlines on the upper-right inverted view of the punches 4. Slip the sheet on which the punch-shank circle

Fig. 17·19. Steps necessary in selecting a suitable die set fo : specific die design: determine punch shank diameter, ( 1); draw ce·ter lines, {2); transfer centerlines to punch ho lder view, (3); c-: superimpose punch shank circle drawing on punch hol der view, ' ,


197

5

6

A

10 Fig. 17·19. (cont.). Steps necessary in selecting a suitable die set for a specific die design: select suitable die set and draw its views, (9) and complete view of punch holder, (10) .

Fig. 17·19. (cont.). Steps necessa ry in selecting a sui tab le die set for a speci fic die design : inspect su per im posed drawings, (S); change position of su~ e ri mpose d draw in gs, (6); pla ce new center position on punc h holder view, (7); and place new center position on die drawing, (8).

was drawn under the die drawing and move it to the upper-right plan view representing the inverted punches . Apply the center of the circle directly under the inter· secting lines representing the ideal center S. Inspect to establish whether or not all holes to be machined through the punch holder will pass outside of the pun ch shank or inside of it. In the illustration, the punch holder has been turned upside down for viewing the punch shank from the top. Observe that two


19

holes are machined partly in the edge of the pun ch shank . Machining away portions of the punch edge in this manner is considered poor practice 6. In this illustration, relative positi ons of holes and punch holder have been altered so that one of the holes passes entirely within the shank and the other entirely outside of it 7. Referring back to the drawing, slide the sheet on which the punch-shank circle was drawn until it clears holes so that they pass entirely outside or entirely inside of it. The best position found, closest to the ideal center, is shown. Dimension A, the wall thickness between the holes and the outside surface, is made 1/8 inch minimum 8. Transfer the new center to the left plan view of the die by measurement. Always remember that because the punch is inverted, horizontal dimensions are reversed 9. Select a suitab le die set and draw its views. Observe that the die block is slightly off center, but that it is positioned as close to the ideal center as possible 10. Complete the view of the punch holder. Front and side section views are then drawn by projection. In actua l practice, the foregoing steps can be performed quickly. They provide th e logical method of selecting a suitable die set fo r a specific die design.

recorded in a standards book for future use. In this illustration are given a ll dimensions which are not ordinarily li sted in die-set catalogs. These dimensions may be used di rectly when applying the views of the die set to your drawings. 0

0

0

0

0

0

0

0

0

0

0

2

3

17-20. CENTER OF CUTTING LOAD When blanks are large, the cutting loads may be great and unbalanced. The center of cutting load must be determined before selecting the die set. This then represents the ideal center, the one we would use if no punch-shank interference existed. To determine the center of cutting load: Step 1. Draw the scrap strip for a die in wh ich cutting loads are unbalanced Step 2. From heavy cardboard, cut blanks and slugs the sizes and shapes of all cut-out portions. Leave thin webs between blanks to maintain relative positions or paste thin strips across them Step 3. Place a square or rectangle of cardboard over a pivot and move it until it is in balance Step 4. Position the cut blanks on the cardboard and slide them until they balance. The point of balance will be the cente r of cutting load or close enough to it for practical purposes.

4

n

n

n

Fig. 17·20. Method of determining center of cutting lood.

17-21. MISSING DIMENSIONS Study of any die-set catalog will reveal that a num ber of dimensions are not given. There are three ways of establishing dimensions which are not listed in a catalog: 1. Dimensions may be estimated. Those dimensions which are no t listed are not critical and may be approximated to proportions printed in the catalog 2. Dimensions may be established with proportional dividers. The point relationship of the divider arms may be set to one of the given dimensions . Points are transferred from the catalog views to the views of the drawing 3. When a component must be drawn at frequent int ervals, missing dimensions may be measured and

Fig. 17-21. Dimensions not ordinarily listtJ in die·set cato lo;'


199

4--,_------------------~~ ~

5

2

6

3

4-4

7

Fig. 17·22. Steps taken in laying out a die set : represent left and right sides of die set with vertical lines, (l); re present front of posts and fron t of die set with horizontal lines, {2); drew circles to represent post posts, (3) and drew circles to represent post bosses, (4). Steps token in layi ng out a die set: block out remainder of die set with light lines, (S); draw smel l orcs wi th heovy lines, {6) ; and da rken all remaining li nes, (7) .

17·22. DRAWING THE DIE SET A proper working procedure reduces loss of time in laying out die sets. Seven steps are required: 1. As we have developed the layout in Fig . 17-19 so far, the left and right sides of the die set have been

represented by vertical li nes, as shown in the illustration 2. In addition, the vertkal center of the die set has been established. Note that preferably the die would be centered between the posts and the front of

200


the die set. Look up this dimension in the catalog and draw horizontal lines to represent the front of the die set. Dimension A between posts a nd die block should be 5/ 8 inch minimum, to allow clearance for the grinding wheel nut when the die block is sharpened. 3. Look up the distance between centers of posts and their diameters and draw circles to represent them 4 . Look up the radii of post bosses and draw them with Hght lines 5. Block out the rest of the die set with light lines 6. Draw all small arcs with heavy lines using a radius template 7. Darken all remaining lines to final object line width. The punch holder is drawn in the same manner. Less time will be required because it does not have clamping flanges.

In the next operation the bo lting flanges a re milled as at B. A five inch diameter cutter is employed, and therefore a 2Y2 inch radius is left at the end of the cut. Corners of the cutter are ground to a 1/8 inch by 45 degree chamfer, and a corresponding angle would be left in the corners of the die holder.

17·23. VIEWS FOR CAST DIE SETS

Fig. 17·24. Steel die sets ore firs t flame cut to shape (A) ; then bolting flanges are mi lied, (B).

Four views are drawn of a back-post die set made of semi~steel or cast iron. These are the views ordimarily shown on a die drawing. Observe that the punch holder and die holder are castings and therefore radii are applied to all comers where the adjacent surface has not been machined. Comers of guide post bosses and of the flange are given large blending radii, a characteristic of this type of die set. The punch ho lder at the upper right has been inverted and therefore the punch shank appears as a dotted circle. Because bushings are viewed directly, they are represented by two solid circles.

17~25.

VIEWS FOR STEEL DIE SETS

Here a re the four views of a steel die set. Campa· rison with the views of a semi-steel die set will reveal three significant differences . The first is the large radius A, and it is 2'h inches. Another is the absence of a flan ge at the back of the die holder B, and a thirc is the smal l angle C, applied in the corner of the milled cut. It is drawn 1/8 by 45 degrees. Whenever a steel die set is selected, the views should be draw. in this style and to propor tions given . In addition. sectioning for steel would be applied. B

@

@

Fig. 17-23. How fou r views of a cast bock -post die set ore shown on a drawing.

17-24. STEEL DIE SETS Steel die sets are drawn somewhat differently and it is necessar y to understand the method of manufacture to draw them prope rly. The first step in producin g a steel di e holder is to flame-cut the shape from plate as at A. Note that edges have s traigh t sides all around, and that the plate from which it is cut is the die-ho lde r thickness with allowance for machining. In actual practice, a number of blanks would be cut simultaneously in an automatic flame cutting machine, with the cutting heads guided by a template.

Fig. 17-25. How fo ur vi ews of stee l bock-post die set ore sho,.on a draw ing .

17-26. SECTIONING The front view and also usually the side view die drawings are sectioned to reveal internal construction. The first step in sectioning is to draw lines at : degrees across die set surfaces in contact with cutting plane to indicate that they have been cc · Inclination of section lines for the punch holder a:.: die holder should be opposite, as shown at A. This !5' importan t for balance. If section lines for both a:=

201


inclined in the same direction, an optical illusion is introduced and the view will appear to lean. Section lines for other details are then drawn, altern ating thei r di rections from top and bottom toward the strip, as at B.

The die set note should contain the following information: 1. The detail number, applied within a detail circle 7/ 16 inch in diameter 2. Manufacturer's name followed by the words "die set'' 3. The catalog number 4. The type of bushings 5. Diameter and length of guide posts. The die set note is applied in a clear space near the centP.r of the die drawing.

17-29. DIE SET STAMP B

A

Fig. 17·26. How sec tion lines ore drown in a die drawing.

17-27. SPACING OF SECTION LINES Draw section lines for die sets to the following proportions: For semi-steel die sets, position them approximately 5/ 8 inch apart, as shown at A. For s tee! die sets, draw section lines in sets, 3/ 16 inch apart. The sets are positioned with about 5/ 8 inch between them, as at B. When section ing combination die sets, those with a semi-steel punch holder and a steel die holder, app ly appropriate section lines to indicate material.

In anothe r method of specifying die set information, a box is printed on the drawing sheet with a rubber stamp and information is lettered in the spaces provided. Stamps are available from die set manufacturers and they vary somewhat in detail. You will notice from the example that some dimensions are not absolutely necessary for standard die sets. However, applying extra dimensions s uc h as those for die space tends to reduce errors because a mistake in specifying the catalog number would be discovered.

DIE SE T DAT A g~\~~iES,

?.~9_~ .:~.1........ COMMERCIAL •••• :::-::::::::: . . .... . DIE SPACE -- A .............. ~-~~--- ····· · ·· ····· B ............ 13................. . L[ ' l TO 11110Hf 'l't ONT TO U C( PRECISION ....

I 1/4

I t.-2

THICKNESS -- J ···;;i";,oroio................ ...... K ...;u;;c;,"·~ocoio" ··· ....... . GUIDE POSTS -- L .......................... ~.~t.~.............................. .. OV!JIIAl\, I.. EP101'H BUSHINGS -- TYPE ............ ~!.~-~ --- --!?~~~':-.?~~- .................... . SHANK -- DIA . ......... ! .~~~........... LENGTH ...........? ?~

........... .

,, JfONf. IS .__(QUIIIIID ST..T£ NOH(

ORDER

FROM

OANLY MACHINE SPECIALTIES,INc. 2100 So. LARAMIE AVE., t Or l'l t or e n

A

8

CHIC AGO

~0.

ILLINOIS

lr11,. ,,. Ort •( I J

Fig. 17·29. Filled in rubber stamp print may be used to specify die set data on drawing.

Fig. 17·27. Proper spacing of section lines.

17-30. MACHINING THE DIE SET

17-28. LISTING THE DIE SET In the bill of material, the die set is always given detail number 1. The information to be specified is too lengthy for the space available in the bill of material, and is therefore given in the fo rm of a note on the drawing itself, as at A. The box i n the bill of material is filled in as shown at 8 , and the reader of the d rawing is thus refe rred to the note . OANLY

OlE SET

There are two methods of applying holes in the die holder for passage of slugs. At A, slug relief holes a re machined with straight walls. Dimension C is 1/ 16 inch for blanks up to No. 16 gage (0.0625 inch), and proportionately more for thicker blanks . The method shown at B is prefe rred for blanking and pierci ng soft materials, which have a tendency to stick together an d fo rm thick slugs which could jam. The holes i n the die set are die filed to the same angle applied to the die block for relief.

CAT. NO. 0603-AI STEEL SHL D. BUSH. I" DIA. X 5 114 GU IDE POSTS

A S PE CI FIC ATION S

SEE NOTE

B Fig. 17·28. Die set on o drowi ng is de sc ri bed in a note, (A) and listed as ~ etoil 1 in bill of materia l, (B) .

B Fig . 17-30. Two methods of app lying holes for the passage of slugs.

202


17-31. STRIPPER BOLT HOLES Counterbored holes for stripper bolts should be proportioned carefully because considerable pounding occurs against the bottoms of the counterbores in operation of the die. Also, a spring stripper may occasionally stick or become jammed. When this happens , a pry bar is used to free it and the stripper then slams up with all the stored energy in the springs. Apply the following minimum proportions: Dimension A = Strip thickness + Grinding allowance . . B = D for a semi-steel. die set D1mens10n % D for a stee 1 die set

I

I I I I I

I I

I I

I

I I

I

I

---,

I I

, ---J

I

I

I

I

Fig. 17·33. Slot machined in the underside of the die holder fac il i· tates remova l of blanks when hole in bolster plate is too small.

17-34. KNOCKOUTS When a large spider knockout is incorporated in the design of the die, it can be flame-cut directly through the punch holder of the die set. A steel die set must be specified, and the flame~cutting is done by the die-set manufacturer before stress relieving and accurate machining . After the spider has been cut fro m the punch holder, it is machined thinner to allow travel and then it is re-inserted in the punch holder. Th e knockout pin s are retained to the spider and knockou t plate by socket cap screws . Fig. 17-31. Proportions of counterbored stripper bolt holes.

17-32. PROJECTIONS All projections in a die block must be supported by corresponding projections applied to the die holder. In this illustration, the dotted lines represent the hole machined in the die holder for blank removal. Observe that the die block projections are well supported to prevent overhang and possibl e breakage under pressure.

Fig. 17·34. Lar ge spider knockout of this stee l die set has bee· flame -cut from the punch holder of the die set.

,w ----. ,-----. -

I

I

I

I

L ___ .J

I

I

I

I

I

I

I I I ~ --- -

,. - - -., I r :;..'

I I 1

'1...:- - - - "'

Fig. 17·32. Al l pro ject ions of this die block are supported by simi lar pro jec tions in th e die holder.

17-33. SLUG SLOTS When the hole in the bolster plate is smaller than the blank, a slot may be machined in the under side of the die holder. At the rear of the die set, it is made slightly wider than blank size. At the front, it need be only wide enough to accommodate a thin bar for pushing blanks to the rear of the press.

17-35. TWO POST DIE SETS Most dies designed for hand feed ing of strip are provided with two guide posts applied at the back of the die set because this type gives maximum visibil i ; and accessibility since it is open on three sides. A back-post die set is also used when scrap stock is to be employed for producing small blanks. Scrap materi ais usually very irregular in shape and other guide post arrangements would interfere with posi tionin . There are three distinct types of back-post die se s : 1. Regular. This is employed for dies with average proportions 2. Long, This type is us ed for dies which are long and narrow 3. Reverse . This type is used for dies which are relatively longer in measurement from f ront to bac·· than their measurement from side to side.


203

2. Large, semi-steel die sets ranging from 22lh by 6 to 25 by 14 inches have sides wider than the distance over the posts, as shown. 3. The larger ranges of stee l die sets are made square or rectangu lar in shape 4. Many dies have relatively small punch members which occupy little punch holder room. For such dies , die sets with V-shaped punch holders provide a better proportioned design as well as greater visibility for loading and unloading work 5. For round pu nch members a round die set may be used.

17-37. THREE-POST DIE SETS The addition of a front post to a back-post die set provides increased stability for unbalanced cuts and when greater precision is required. These are incorporated only in square or rectangular steel sets. For ha nd feedi ng, the extra post is applied at the front, left corner as at A. When the feed is automatic, it is centered as at B.

2

3 Fig. 17·35. Three types of back ·post die sets: reg ular, ( 1); long, {2); and reverse, (3) .

17-36. STYLES Back-post die sets are made in five different styles or shapes: 1. This style is the most common . It is used for small medium-size die sets ranging from 3 by ::1 inches to about 16 by 18 inches in both semi-steel a nd steel

Fig. 17·37. Three·post die sets lor hand, (A) and automatic, (B) feeding provide more stability.

17-38. FOUR-POST DIE SETS Large die sets are ordinarily provided with fou r posts. There are two styles : At A is illustrated the con-

0

0 2

0

0

0 3

4

0

0

5

Fig. 17·36. Five styles of back · pos t die sets.

Fi g. 17·38. Large die sets hove four guide posts, some having slots at side, (B) to prevent sl ippage as the die is lifted.


204 ventional type with unbroken edges, employed for small and medium-size four-post sets. A.t B is shown the safety type provided with chain slots milled into the sides to facilitate Lifting the die with a chain fall. The slots prevent possible slippage as the die is lifted. For foolproofing, one post may be offset 1/ 8 inch towards the edge of the die set, or one post may be made over-size. This prevents accidental reversal in assembly . Four-post sets are not sui table for hand feeding. They should always be used in conjunction with an automatic feed. They are now widely employed for progressive dies and carbide dies because they provide rigidity.

available in semi-steel in the sty le illustrated at A, and in steel in the style shown at B. Components may be supplied in combination, with a steel die ho lder used in conjunction with a semi-steel punch holder as at C. Another important application for center-post die sets is the performing of secondary operations on workpieces havin g a right hand and a left hand. P arts of one hand may be conveniently loaded from one side. When the other hand is to be run, the die set is turned around 180 degrees in the press for ease in loading.

17-39. LONG, NARROW DIE SETS This type of die set is used to retain dies for cutti ng, bending, and forming of long, narrow parts. They are back-post sets, and they are available with either two or three guide posts. Two posts are specified for sets ran ging from 12 to 72 inches in length, and three posts for sets ranging from 84 to 240 inch es in length.

Fig. 17·39. Die set for cutting, bending and forming of long, narrow parts.

17-40. ROUND DIE SETS These die sets are selecte, for retaining round dies such as drawing dies, trimming dies, and th e like. There are two styles: Back-post sty le as shown at A and center post style as shown at B are available in diameters ranging from 4 to 48 inches.

0

0

Fig. 17-41. Die used for secondary operation work such as pierc ·- ; and coining.

A

B

Fig. 17·40. Die sets fo r drawing and trimming round pa rt s.

17-41. CENTER-POST DIE SETS These die sets are ordinarily employ ed for secondary-operation work such as pie rcing, coining, and the like. Parts are loaded from the front. The die sets are

17-42. FOOLPROOFING Center-post and diagonal-post die sets a re provtr..E":: with different-diameter posts , dimensions A and 8 Thus, the pun ch holder cannot be reversed on th e · ; ~ holder. This is an important precaution for symme c=.... dies.


0

0

205

punch holder, therefore, is actuated independently of the press slide. Long shoulder bushings should be used with these die sets because, in operation, the guide posts must always be guided within them.

0

17-44. LARGE DIE SETS- SEMI-STEEL Large semi-steel die sets are available in the back post A, center post B, diagonal post C, or four post D styles. All are provided with clamping flanges for mounting in the press. They are assembled with stee I shoulder bushings unless otherwise specified.

8

A

0

0 0

8

A Fig, 17·42. Die guide posts.

sets are faolproofed by using different-diameter

17-43. FLOATING-ADAPTER DIE SETS In blanking and piercing thin stock and for shaving and broaching operations, very little clearance can be allowed between punch and die members. The slightest lateral movement would cause nicked or dulled cutting edges. The floating-adapter shank A is clamped in the ram of the press in the regular way. However, by using this adapter the ram can only impart an up and down motion to the punch holder. Any inaccuracy or wear in the slide of the press will not be transmitted as stresses on the die set guide bushings and guide posts. The

Fig. 17·43. Die set with floating adapter shank, (A), prevents lateral movement of punch holder normally the result of inaccuracies in the press slide.

Fig. 17·4 4. Four styles of large semi · steel die sets.

206

17-45. LARGE DIE SETS- STEEL Large steel die sets are made of plate. They have ground surfaces and they are square or rectangular in shape. Two-post sets are given one of three post arrangements. At A is shown the back post, at B the center post, and at C the diagonal post sty les. Sizes a re not limited. That is, they may be specified to any length, width, and thickness of punch holder and die holder.


ro

0

I 8

La

0

r:~ DIE SPACE A 15 30 45 60 75 90

105 120 135 150

I

B

10 20 30 40 50 60 70 80 90

100

PUNCH HOL DER THICKNESS

DIE HOLDER THICKNESS

c

D

I 114

I 1/ 2 2 2 1/ 4

ll

I J/4 2 2 I •2 3 3 1/ 2

4 4 I 2 5 5 I 2

J 3 1/ 2 4 4 1/ 2 5 51,2

6

FORCE

lN TONS

0 10 30 50 70 90

110 130 !50 200

10 30 50 10 90 110 130 150 200 11\' ('f

Fi g. 17·46. Tobie for determin ing punch ond die ho lder thickness.

17-47. HEAVY-DUTY DIE SETS

Fig. 17·45. The three pos t arrangements of Iorge two-post steel die se t s.

This type of die set features a n exceptionally large and thick die holder, which in effect becomes the bolster plate of the press. Heavy-duty die sets are particularly useful for long production runs. They are assembled with removable boss bushings to provide adequate alignment between punch holder and die holder.

17-46. RECOMMENDED THICKNESSES The die holder and punch holder of a la rge die set must be gi ven sufficient thickness. Die set catalogs recommend specific thicknesses in relation to side-toside and front-to-back dimensions and these recommendations should be followed. When plates are too thin in relation to their width a nd length, they will warp causing misali gnment of punch and die members and binding of guide posts in guide bushings . Conversely , when plates are too thick the overall die cost increases. This table provides a useful guide to the specification of punch holder and die holder thicknesses. Observe that there are two considerations, the die-space dimensions A and B, and the force in tons required to perform the work that is to be done by the die . Select the values for C and D opposite whichever is gre ater. 'Examp le: If the die set area for a particular die measures 30 by 20 inches and the force in tons is less than 30, the values of 1% inches fo r C and 2 inches for Dwould be selected. However, if the fo rce in tons were 60, we would use the values opposite pressure in tons of 50 to 70, and the value for C wo uld be 2Y2 inches and for 0 3 inches.

Fig. 17·47 . Typical heovy·duty die set.

SPECIAL DIE SETS Despi te the large number of sty les and sizes · standa rd die sets available, it is occas ionally n~ essary to design a special die set for a specific jo: This occurs particularly for parts which are exce;::ionally large or which con tai n severe offsets. Pro\ · ·= adequate strength by app lying ribs or gussets ~= highly stressed sections. Specific rules c anna -= given because of the variety of conditions encounte e: Special die sets are designed by the die desi gne: and a print is sent to a die set manufacturer where die set is actually built.

Section 18

DIMENSIONS AND NOTES study of trigonometry will be a practical one. We will employ it as a tool for solving specific problems, and charts will be provided for simplifying the subject and to avoid the requirement for memorizing functions or formulas .

After the layout of a die has been drawn, dimensions and notes must be applied to complete the information that the diemaker will require in order to build the die exactly as the designer planned it. Some dimensions are simple; others must be calcu lated from considerable background information and experience. There are two methods of detailing a die. In assembly detailing, all dimensions and notes are given on the assembly drawing. The dimensions can be of two kinds. The first includes dimensions that establish relationships between the various components, as needed for assembly of the die. Additional dimensions are a pplied for critical operations performed after assembly to maintain accu racy. Assembly detailing is used for die designs that are well adapted to employment of the method because of the procedure which must be followed in building the die . The second method of detailing is to draw and dimension each component individually. Separate detailing is used for more complex dies, and it is the best method in most cases because the die maker can be furnished with more complete information. Dimensions should not have to be calculated in the toolroom, because while the diemaker is working on dimensional problems his expensive equip~nt is standing id le. The shut height of the die, that is the distance from the top of the punch holder to the bottom of the die holder should always be given on the drawing. It is noted with a fractional dimension followed by the abbreviation S.H. for shut height. Fractional dimensions on the part print are converted to decimal dimensions on the jig borer layout. This ensures that the die will produce parts well within the required limits. Decimal dimensions are given to three places ordinarily. The ten thousandths in the fourth place are left out if they number less than five. When there are more than five, the number in the third place is increased by one. If the numeral in the fourth place is a five, four places may be gi ven.

18-1 . RIGHT TRIAIIIGLES Most problems encountered in die design involve the solution of right triangles. A right triangle has a 90-degree corner as shown at A. The inclined line is the longest of the three and it is called the hypotenuse. The side directly across from any given angle is called the side opposite, while the side nearest to a given angle is called the side adjacent, as shown at B and C.

A

8

SlOE AOJACfNT

GIVEN ANGLE

TRIGONOMETRY For applying dimensions to die drawings, it is freque ntly necessary to compute problems involving trigonometry. This is the determination of unknown sides or angles of triangles. Our approach to the

Fig . 18·1. Terms reloting to right tri angles.

207

OTES

208 18·2. GRAPHIC REPRESENT AT ION In this illustration, those functions of angles that we will use are represented graphically. A circle is drawn with its center at the large apex of a triangle. A vertical line is extended downward from the intersection of the hypotenuse and the circle, line length A, and another vertical line from the outside of the circle, line C . The following, then are the functions of the angle (designated with the circular arc) of the right triangle whose hypotenuse is the radius of the circle with a valu e of 1: A- sine B- cosine C -tangent D - cotangent.

are marked Sine, Cosine, Tangent, Cotangent, and other less frequently used functions. For a whole number of degrees, that is, one without minutes or seconds, read the function directly on the top line as for instance, 20 ° - 0 minutes. When the number of degrees is followed by some minutes, tum to the appropriate page and read down the M column to the given number of minutes. Functions are then read on that line. For instance, the tangent of 20°32' would be 0.37455. Angles from 45° t o 90° are listed at the bottoms of the pages and minutes are read upward in the column at the extreme right. Names of functions are located at the bottoms of the columns and you must trace upward to the line for the appropriate number of minutes for reading values.

B

Q

Fig. 18-2. Graphic representation of the functions of on angle of o righ t triangle.

18-4. IDENTIFYING KNOWN AND UNKNOWN SIDES AND ANGLES

18-3. MATHEMATICAL RELATIONSHIPS The functions of right triangles may be calculated by the following formulas: 1. The sine of an angle is equal to the side opposite divided by the hypotenuse.

.

sme

A a

. B = -b stne c

''c

2. The cosine of an angle is equal to the side adjacent divided by the hypotenuse. cosine

A = ~c

cosine B = ~ c

3. The tangent of an angle is equal to the side opposite divided by the side adjacent. Q

tangent A =b

tangent B

=-;;-b

4. The cotangent of an angle is equal to the side adjacent divided by the side opposite. cotangent A =

~

Fig. 18-3. Letter designation s for use in calculating functions of a right tria ngle.

cotangent B = ~

In actual practice, functions of triangles are seldom calculated. Instead they are taken directly from a table of trigonometric functions in a handbook such as MACHINERY'S HANDBOOK. Make sure that you use the table entitled ' atural Trigonometric Functions' and not the one entitled 'Logarithms of Trigonometric Functions'. For angles from 0 to 45 degrees, the table is read downward. At the top of the page the number of degrees is given in bold type, as for instance, 20 °. The left column, marked M, lists minutes from 0 to 60. At the top of the page, above the columns of numerals

It will be necessary to learn the method of identifying the various sides and angles. In the illustration , observe that capital letters denote angles and lower case letters denote sides as follows: A - acute angle B - acute angle a -side b -base c -hypotenuse. In our method of identification, a heavy black line denotes the side or angle to be calculated and double lines indicate other unknown sides and angles. In the exam ple, the side a would be the one requiring soluti on. Side b would be unknown. We would therefore know the values for angle A, angle B, and hypotenuse c, and i: would be a simple matter to solve for the value o • side a as will be shown.

B

<1

b Fig. 18 -4. So lid black side a of right triang le is the side to be cc · culoted. Double lin es indicate side b is un kno wn. Hypotenu se ~ and angles A and Bare known.

209

TRIGONOMETRIC EQUATIONS HEAVY LINES REPRESENT SIDES AND ANGLES TO BE CALCULATED DOUBLE LINES REPRESENT OTHER UNKNOWN SIDES AND ANGLES

1 a =~c - b2

SIDE

a B

a= c x cos B

·~

b

B

a = b x cot B

b

b

b =Vc2- a2

·~

b "' c x sin B

~ b

B

X

b "' axtanB

b

b

A

b =ax cot A

·~

·~

A

cos A

b

A

a

HYPOTENUSE

c

b =c

th.

b

B

a=bxtanA

·~

·~

BASE

b

·E:h..

·ltb,.

90"

a= c x sin A

0 ~slnA

·~

A

b

b

8

~slnB b

b

~c~A b

A

Fig. 18·5. Trigo nometric equations used in computing sides and angle s of tri angles.

First however, we must know exactly what i nformation will be required befo re any triangle can be solved. To compu te the l ength of one side of a triangle, the length of the other two sides must be known or the length of one side and one acute angle must be known . Given this information, we can determine the values of the other sides and ang l es .

18-5. TRIGONOMETRIC EQUATIONS This chart has been prepared to provide a simple method of selecting equations in the solu tion of

trigonome try problems. L et us enter into a careful analysis of its features because this will enhance i ts value to you in the development of orderly methods. Note th at the block at the top of the first s heet is composed of five rectangles within which a re enclosed triangles. It is labeled 'side a ' . In every one of these five triangles, side a is th e un known side, the one requi rin g solution. In the first triangle , sides b and c a re known. Angles other than the 90 ° angl e a re unknown and they are identified as such by double lines. The formula to employ in solving for a when only the bas e

DIMENSIONS A D NOTES

210

ANGLE

cos A = ~c

~ b

A

·~ b

t

A

a = b x sin A sin B

~

A

A = 180° - (B + C)

cot A= E

·~ b

c/t&.. sin A = a x sin B B b

b

A

cos A = ba + c 2. -a z 2xbxc

u b

a

A

B = 90" - A

B

b=

ax sin B sin A

'b. b

A

c = b x sln C

~nB c

A

b

C = 180°- (A + B)

B = 180•- (A + C)

B

B

B

~

A

~.

B

b

tan A=

B

ANGLE

B

·~

~.

A

sin A=~

A = 90"- B

B

C~A sin B = B

b x sin A a

~ b

A

cos B = aa + c z.- b e 2xaxc

n b

C/t&.A sin C = B

c

h

c x sln B b

b

2 b2 l cos C = a + - c 2xaxb

n

c

b

Fig. 18-5. (cont.} Tri gonometric equati ons us ed in computin g si de s and angle s of trian gles .

b and hypotenuse c are known :s given above. In the second triangle, only angle A and hypotenuse c are known and the formula is given when this condition is present. The s ame method is followed for the succeedi ng trian gles, and formulas are given for the various combinations of kno wn and unk nown sides and angles . In the next block of triangles , formulas a re given for solving for the unknown base b, and in the third block for the hypotenuse c. At the top of th e next group of triangles formu las

are given for solv ing for angles A and B. Underneath this, formulas are given for solving for oth er than rightangle triangles . Observe that in every instance th e angle known, the on e used in the formula , is identified on the triangle by a s ingle thin a rc.

DIE TRIGONOMETRY The solution of problems in tri gonometry is a simp le procedure when formulas given in Fig. 18-5 are understood and employed. It is not always so simple to se up or iden tify the triangles that will require solution

211

DIME SIONS AND NOTES

for applying dimensions to drawings of dies. This is because most blanks have to be nested or inclined to conserve material. Establishing the triangles that will require solution can be difficult unless you acquire a clear understanding of the entire process of triangulation. The following outline or guide will increase your kno wledge of this important subject.

18-6. PART DIMENSIONS

dimensions in the same manner as shown here. All internal radii in the die-hole contour are completed as full circles with phantom lines. Notes with leaders are employed to indicate that holes are to be jig bored at those locations. Observe that horizontal dimensions A and B, and vertical dimensions C and D cannot be applied directly from dimensions given on the part drawing because of the inclined position of the blank. Their lengths must be calculated.

On part drawings for sheet metal workpieces, dimensions are normally applied horizontally and vertically as shown at A for a simple representative part. Note that a triangle is formed as illustrated at B. The unknown dimensions of this triangle can be easily calculated by trigonometry because its base and side have been given.

1-------A-------~---8--~

0

0

A

B

Fig. 18·6. App lying trigonometry to port drowing to solve for un· known dimensions.

18-7. SCRAP STRIP This is a good scrap strip design for the part illustrated in Fig. 18-6. The blank is drawn in an inclined position to conserve material. Angular positioning of workpieces is required for most parts except simple round, square, or rectangular blanks, which may be run side by side, positioned either vertically or horizon tally.

Fig. 18·7. Scrop strip de si gn for port shown in Fig. 18·6.

18-8. JIG BORER LAYOUT Holes in die blocks are dimensioned for jig borer layouts. In this type of dimensioning, all horizontal dimensions are given from the line representing the left surface and all vertical dimensions are given from the line representing the upper surface. Grind marks are applied to extension lines to indicate surfaces from which accurate measurements can be taken. In a variation of the method, the first hole is located with fractional dimensions, both horizontally and vertically, Other holes are then located from it with decimal

.625 BORE THRU 3 HOLES

Fig. 18·8. Typical dimension ing of die block for jig bori ng operation.

18-9. DIE BLOCK At A is shown the plan view of a die block after holes have been jig bored. Note that the large holes will form part of the actual die-hole contour or outline. ] ig boring holes to produce internal radii provides a very accurate beginning or basis for laying out and machining irregular die holes. Precise lines are scribed tangent to the jig bored holes . The center is sawed out in a metal-cutting band saw, and the sides are then accurately die fi led to "split the line", thus completing the opening as shown at B.

18-10. TRIANGLES IN DIE DIMENSIONING When a part is tilted for best nesting in the scrap strip, Fig. 18-7, many dimensioning problems can occur when preparing the jig borer layout. Note that when the inscribed triangle is tilted, and horizontal and vertical lines are drawn from the vertices of the acute angles of the inscribed right triangle a second and adjacent triangle is produced. Tilting the part shown in Fig. 18-6, with its triangle established by the vertical and horizontal dimensions produces this effect. Observe carefully the arrangement and direction of adjacent right triangles formed. Their positions will depend upon the direction and inclination of the part in the scrap strip.

212

·DIME SIONS AND NOTES

FORMULAS

00

FOR

ADJACENT TRIANGLES

TRIGONOMETRIC FIGURE IS SHOWN IN EIGHT POSITIONS TO AID IN VISUALIZING APPLICATION,

0

0 B

0

0

00 A

·~~·

BW A

A

C = A cos X + B sin X

8 Fig . 18-9. Plan view of die block after jig boring, (A) end after bcndsawing and die filing, (B).

EJXDB

D = A s in X-Bc ls X Sin X = BC + AD

~

A~~A B

Fig. 18·11. Chart tr iang les.

08

B = C s in X • D cos X

C B&x

A

~X

A = D Si n X + C cos X

XC

c

B

which

A

B

gives

formulas

for

solving adjacent

and the numerous positions which triangles may assume. Therefore the trigonometric figure is shown in eight positions to aid in visualizing application.

18·12. ENLARGED LAYOUT To establish triangles, draw as large a layout of the part as possible to be certain that small triangles will not be overlooked. The sides of some of these triangles may be only a few thousands of an inch long and would not be detected on an actual -s iz e drawing. If they are ignored, final dimensions on the jig borer layout will be incorrect. For most sma ll

Fig. 18·10. A second ad jacent triangle is constructed by drawing horizontal and vertical lines from the vertices of the acute angles of the inscribed right tr iangle which wil l facilitate dimensioning of jig borer Iayaut.

18-11. SOLVING ADJACENT TRIANI.iLES You will find this chart in valuable in the solutions of adjacent triangles. Formulas are given forsolvingall the sides and also for determining the large angle X when sides are known. It is often difficult to establish triangles on drawings because of the confusion of lines

~------- u --------~

Fig. 18·12. Enlarged part layout lor determin ing dimensions jig borer Iayout.

«

DIME

OTES

blanks a ten-to-one layout will be satisfactory. It is a convenient scale because dimensions for the large layout are established by simply moving the decimal point one numeral. For example, an actual dimension of 0.093 would become 0.930 on the ten-to-one layout. Another reason for making a large layout is that it provides a check for accuracy of calculated dimensions. Scaling the layout will often reveal mistakes which might otherwise remain undetected. After the layout has been drawn, fasten a s heet of thin tracing paper over it with drafting tape. Triangles are established on this outer tracing paper. Often the paper will become covered with numerous lines before it is discovered that a wrong start was made. When this happens the tracing paper can be removed an d a new one substituted. The layout itself will not be marked and it need not be redrawn. Draw the first triangle and identifying letters and dimensions with black lead. Succeeding triangles may be drawn in different colors to help in identification. The practice in most tool design offices is to establish all triangles which will require solution, set up formulas for the entire job, and then "run them off" on a calculator. In establishing triangles on the tracing paper or tissue, observe the following ge neral rules: 1. Connect centers of circles with light lines 2. From centers draw horizontal and vertical ex tension lines. These may complete required right triangles 3. Extend oblique lines until they inte rsect horizontal and vertical lines to define triangles 4 . Add vertical and horizontal dimensions to establish lengths of longer lines which may become sides of. larger triangles S. When two triangles have a common side or angle, solution of one triangle may form the basis for solving the other 6. When two circles are tangent to each other, the distance between centers is the sum of the radii 7. When solving for centers of arcs, it may be helpful to draw the full circles 8. When a line is tangent to a circle, draw the following two lines in attempting a solution: a. The radius to the tangent point b. A line parallel to the line of tangency and through the center. This line usually will be helpful when the angle made by the tangent line is known 9. When making a ten -to-one layout , first draw the part in the position in which it is dimensioned on the part print. Draw circles to rep resent all holes and draw all portions of circles th at form a portion of the part outline or are contained wholly within the part outline. Through the centers of thes e circles or portions of circles, draw long vertical and horizontal lines 10. Unfasten the sheet and rotate it to the selected angle of tilt. Then draw horizontal and vertical lines through centers to establish triangles for solution . At the same time, draw strip edges to establish final stri p width. In Fig. 18-12 you will note that angle X is equal to the angle of tilt, and that angle P is its completement. Solutions for values A and B of adjacent t riangles 1 and 2 are determ in ed by form ulas given in Fi g. 18-11. In all , three separate triangles are formed, numbered

213

1, 2, and 3. Following is the procedu re for solution: Solve for A and B Given C, 0, and X: Given D and P: Solve for E and F Final dimensions are determined as follows: A is read di rectly B is read directly T equals A- E U equals B + F.

18·13. MULTIPLE TRIANGLES When the corner radius of a part similar to t he one shown in Fig. 18-12 is small, other triangles must be solved before jig borer dimensions can be determined. Taken together, views A and B illustrate perfectly th e number and often difficult arrangement of triangles which re quire solution for even relatively simple workpieces. It should emphasize the need for a large layout and systematic methods of operation . View B is an enlarged portion of view A to reveal small triangles more clearly. Observe that six separate triangles are established. Angle X is the angle of tilt. Angle P is

T

1---- - - -

u - - - - -------i

A

c

F

3 D

8

B Fig. 18·13. Enlarged part layout in which mult iple tr iang les are use d for determining di mension s for jig borer input.

OTES

214

its complement and angle R is a Angle Q may be found by subtracting ing is the procedure for solution: Given C, 0, and X: Solve Given D and P: Solve In enlarged view B: Given G and R Solve in triangle 4: Solve Given J and S in triangle 5: Subtract K from H to Solve Given L and Q Solve in triangle 6:

45-degree angle. P from R. Followfor A and 8 fo r E and F for H for K for L for Mand N

Final dimensions are determined as follows: A is read directly 8 is read directly T equals A - (E + N) U equals B + F + M

18-14. DIE CLEARANCES Another factor must be considered in applying die dimensions. This is the amount of clearance between punch and die members. For a blank to part cleanly from the material strip, there must be exactly the correct space between the edge of the punch and the cutting edge of the die. If too little clearance exists, power consumption to operate the press will be excessive. Also, when the punch enters the material strip, the fractures which originate from both sides of the stock - punch side and die side - will not meet,

Constants for Various Materials Formula:

Thickness of Stock Given CollBta.nt

MATERIAL

CONSTANT

Copper .. . . .. ... .. . . . .. .. . .. . 21

and a ragged edge will be formed on the blank, or on the inside edge of the hole being pierced. Excessive clearance will dish the blank and produce long, stringy burrs all around the edge. Application of correct clearances will result in a blank free of burrs, and with the burnished portion of its edge extending to the greatest possi ble depth. This burnished part of the edge should be approximately onethird of the blank thickness. The proper clearance to apply depends upon the material, its degree of hardness, and its thickness. The accompanying table gives the formula and table of constants by which clearances may be calculated. The formula says that the clearance is equal to the stock thickness (in inches) divided by the constant. The \IE!lues arrived at by the use of this table and formula apply to overall clearances or diameters. When clearance "on a side" is desired, as when laying out dies having an irregular contour or for cutting out only portions of a blank, divide the answer by two. For example, if 16-gage (0.0625 inch) hard steel is to be punched in the die, look under Hard Steel in the table, and the constant 14 is given. Divide 0.0625 by 14, and the answer 0. 0045 inch is applied either to the punch or to the die hole. Below the table of constants of Fig. 18-14 is give the punch or die allowance to compensate for par size change. The use of this information is discussed further along under "Secondary Allowances."

18·15. TABLE OF DIE CLEARANCES This table lists clearances directly. The values apply to overall clearances or diameters. Stock thicknesses employed by industry are in terms of gages or decimal thicknesses. In either case, the clearance can be interpolated by reference to values given. For clearance "per side", divide the given amounts by two.

Brass .... . . . ... .. . .. ... . ..... 20

Soft Steel. . . . . . . . . . . . . . . . . . . . 17 Medium Steel. . .. . . . . . .

16

Phosphor Bronze . . . . . . . . . . . . . . 16 Hard Steel . . . . . . . . . . . .

14

Boil~r

10

(over

Plate . .. ...... . .. ~

in. thick)

Soft and Medium Steel. ....... 10 (over

X in. thick)

Aluminum ....... . .

10

(to )1 in. thick)

Aluminum ...

8

(over )1 in. thick)

PUNCH OR DIE ALLOWANCE TO COMPENSATE FOR PART SIZE CHANGE STOCK, THKKNESS, GAGE

ALLOWANCE IN.

50 to 22 ..... ... . .. .

0.001

22 to 16 ... . .. ... . . . .. . .

0.0015

16 to 10. . .. . . . . ...... . .

0.002

Fig. 18·14. Table of constants lor comput ing clearances and tab le of allowances to compens ate for part size change.

18-16. APPLYING CLEARANCES For dies of irregu lar shape the clearance must be added to the required dimension under certain conditions while at other times it must be subtracted from it. This illustration shows how to apply clearances . Clearance is applied to either the punch or the die; never to both. Here is the rule to follow: When a slug is produced to be thrown away as scrap, the punch must be to size and clearance is applied to the die . When a blank is produced, which will be kept, and the strip from which it is removed will be thrown away a scrap, the die opening is made to size, and the clear· ance is applied to the punch. At A is shown a pun c~ and die hole to which clearances are to be applieC:. Observe these rules: 1. When clearance is applied to the punch: Su' tract clearance from all radii with centers inside the punch. Add clearance to all radii with centers outside . Subtract from all dimensions between parallel lines Angles and dimensions between centers remain co~ stant. 2. When clearance is applied to the die: Add clea: · ance to all radii with centers inside die. Subtrac clearance from all radii with centers outside. Add -

215

STANDARD PUNCH AND DIE CLEARANCES STOCK THIC KNESS

SO FT STEE L

MEDIUM STEEL

HARD STEEL

0.0 10 0. 020 0. 030 0.040 0.050 0. 060 0. 070 0.080 0.090 0.100 0. 110 0. 120 a. 130 0. 140 0.150 0. 160 0. 170 0.180 0. 190 0. 200 0. 210 0.220 0.230 0.240 0. 250

0. 0006 0. 0011 0.0017 0. 0023 0. 0029 0. 0035 0.0041 0.0047 0. 0052 0. 0058 0.006 0. 007 0.0076 0. 0082 0.0088 0. 0094 0. 010 0.0105 0. 0111 0. 0117 0.0123 0. 0129 0. 0135 0.0141 0. 0147

0. 0006 0.0012 0.0018 0.0025 0. 0031 0.0037 0.0043 0.005 0. 0056 0.0062 0. 0069 o. 00 75 0.0081 0.0087 0.0093 0.010 0.0106 0. 0112 0. 0118 0.0125 0.0131 0.0137 0. 0143 0.015 0.0156

0. 0007 0.0014 0. 0021 0. 0028 0. 0035 0.0043 0.005 0.0057 0.0064 0.0071 0.0078 0.0085 0 .0 093 ~

0.0 10 0.0107 0. 0114 0. 0121 0. 0128 0.0135 0.0142 0.0 15 0.0157 0.0 164 0.0171 0.0178

STAINLESS STEEL

0.0008 0.0016 0.0024 0. 0032 0.004 0.0048 0.0056 0.0064 0.0072 0.008 0.0088 0.0096 0.0104 0. 0112 0.012 0.0 128 0. 0136 0.0144 0.0 152 0.016 0.0168 0.0 176 0.0184 0. 0192 0. 020

PHOSPHOR BR ONZE

BRASS

0.0006 0.0012 0.0018 0. 0025 0.0031 0.0037 0.0043 0.005 0. 0056 0. 0062 0.0069 0.0075 0.0081 0.0087 0.0093 0.010 0. 0106 0. 0112 0. 0118 0.0125 0.0131 0.0137 0.0143 0.015 0.0156

0. 0005 0. 001 0.0015 0.002 0.0025 0. 003 0.0035 0. 004 0. 0045 0.005 0.0055 0.006 0. 0065 0.007 0.0075 0.008 0.0085 0.009 0. 0095 0.0 10 0.0105 0. 011 0. 0115 0.012 0.0125

Fig. 18·15. Table of standard punch and die draw ings showing how c learances are applie d.

all dimensions between parallel lines . Angles and dimensions between centers remain constant. Let us consider the act ual application of clearances to a die drawing. At B and C are shown a blanking punch within a die hole with clearance greatly exaggerated. ThE> layout at B is a blanking station . Therefore, the die nole must be made to sizes given on the part pri nt and clearances are applied to the punch and it will be sm alter by the amount of clearance. In applying dimensions observe that : · 1. The amount of clearance is s ubtracted from each of the radii A 2. The amount of clearance is added to each of the radii B

COPPER

0.0005 0.0009 0.00 14 0.0019 0.0023 0.0028 0.0033 0.0038 0.0042 0.0047 0.0052 0. 0057 0. 0062 0.0066 0.0071 0.0076 0.008 0. 0085 0.009 0. 0095 0.010 0. 0104 0.0 109 0. 0114 0. 0119

ALUMINUM

0.001 0.002 0.003 0.004 0. 005 0. 006 0.007 0.008 0. 009 0. 010 0. 011 0. 012 0. 0162 0.0175 0. 0187 0.020 0.0212 0.0225 0. 0237 0.025 0. 0262 0. 0275 0.0287 0. 030 0. 0312

clea ran ces and

3. Distances between centers remain the same for both the pu nch member and die hole. The layout at C is a piercing station. Therefore, the punch must be made to sizes given on the part prin t. Clearances are applied to the die hole and it will be larger by the amou nt of the clearance. Observe that the order is reversed. For radii at A, the amount of clearance is added to the radius . For radii at B, the amount of clearance is s ubtracted from the given radius. Distances C remain constant. Until facility in applying clearances is acqui red, it is advi sable to make a similar layout, allowing about 1/ 8 inch clearance be tween lines representing the punch and die members. Dimensioning directly on this layout will reduce the possibility of error becaus e

216

DIMENSIONS AND NOTES

it will be readily apparent whether the amount of clearance s hould be added or subtracted from any given dimension. Cutting faces of blanking punches are fitted to the die and therefore they do not ordinarily require dimensioning. Also, in the plan view of the punches, do not give locating dimensions. The die maker will know that all punches must fit in their corresponding die openings and he will locate them accordingly.

---- --- CONSTANT-----

SUBTRACT

SECmWARY ALLOWANCES -~--_;_ __ "7--CONSTANT·:--::--·-j . '-, . . ,. .

After they have been punched out, holes close in a small amount if they are under 1 inch in diameter . Blanks under 1 inch in diameter have the reverse characteristic and become l arger. A second table in th e lower portion of the illustration Fig. 18-14 lists the amount to add either to the punch, or subtract from the die, to compensate for this , so an acc urate blank wi ll be produced. When the blank is required, the allowance is subtracted from the diameter of the die hole. When accurate piercing is required, the allowances must be added to the punch diameter . For punches and dies of irregular shape, one-half the given value is either added or subtracted all around. Apply the ailowance, then add or subtract the clearance. For example: In piercing a 0.500-inch diameter hole in 16-gage (0.0625) stee l, the allowance (0.002) is added to th e punch and it is made 0.502 inch in diameter . The clearance (0. 004) is added to this dimension and the hole in the die block is made 0.506 inch in di ameter. For a 0.500-inch diameter blank, the allowance (0. 002 ) is subtracted from 0.500 and the die hole is made 0.498 inch in diameter . The clearance (0.004 is subtracted from this dimension and the punch i make 0. 494 inch in diameter. Holes or blanks larger than one inch diameter wi ~ not enlarge or shrink appreciably and no allowance need be applied. When tolerances are liberal, as when hole dimensi onare given fract ionally, make piercing punch diamete: 0.005 inch larger than nominal size. This allow ance takes care of closing in of holes after piercing and o: punch wear. When dimensions are he ld more accurate :· specify punch diameters to the high side of the tolerance

.

A 1---

-----

c

-----~---l

~------- c -------~

A

c

A ~-----c----~~

B ~----------- c ------~~

>----------- c - - ------<-i A

18·17. JIG BORER LAYOUT

A

t--------- c --------~

c Fig. 18·16 Method of apply ing clearances to punch and die hole of a die,

A jig borer layout guides the jig borer operator i machining holes in die blocks and corresponding holefor punches. In this representative layout, note th = arrangemen t of dimensions , all of which are givedecimally. All internal radii that is those with the centers within the large die hole, are complete d a5 fuii circles with ph antom lines and they are speci fie:: as jig bored holes. These accurately positioned hoe: provide a basis for laying out and machinin g '-:= irregular die opening. Center to center dimensions whi would be identical for the punch view and for the rl::: view need not be repeated. On the punch view are gi · only sizes of holes to retain piercing punches a: :: actual punch dim ensions and radii not duplicated on die view.

21 7

signed for them . To acquire a thorough understand ing of the process of blank development, it will be necessary to learn exactly what occurs when metal is bent. This di agram explains the action. Note the following details : 1. That portion of the metal on the side of arc A has been stretched 2. That portion of the metal defined by arc a and shown solid black has been compressed

A

~ +

3. Bending may be considered to occu r along the inside line B. This is the neutral line or axis along which neither stretchi ng nor compression would take place. To determine the length of material in the bent arc, it is necessary to compute the length of arc along the neutral line. For calculation purposes, the distance B will be con s idered as either 1/4, 1/ 3 or 1/ 2 of th ickness T, depending on the size of radi us R. Note tha t addin g A (measured along the neutral axis), C, and D gives the length of the blank.

18-19. BEND DEVELOPMENT To develop a bent or formed blank A in an orderly way, proceed as follows: 1. Sketch a side view or section of the part, to enlarged scale if necessary , an d apply dimension lin es as shown

\_

~l~· e

8 Fi g. 18· 17. Die vie w (A) and pu nch view (B) of a typ ical iig bo rer layou t.

18-18. BLANK DEVELOPMENT

-IN ('")

Blank development entails the designi ng of the flat blanks from which bent, formed, and drawn workpieces are made. The t echnique used is to analyze the finished workpiece and in a series of steps transform it into the flat blank from which it was stamped. The technique is called blank development. The designing of developed blanks is necessary so that di mensions can be properly applied to them and so that cutoff, blanking, bending, or form in g dies can be de-

- '---

__j L#\6

A

GA. (.06 25)

1.0 625-j

1.06251

f c

\()

N

Cii

R

C'l

l Fig. 18·18. Length of blanks is C plus D plus bend A measured along neutral ax is.

2

3

Fig. 18·19. Method of determining blank length.

21 8

DIMENSIONS AND NOTES

and that each requires the use of a different formula . In the first, the arc has a radius smaller than the stock thickness and approp ri ate formu las are given below the illustration. In the second, the arc is between one thickness and two thicknesses of stock, and in the third the arc radius is greater than twice the stock thickness. The upper formulas apply for 90-degree bends, which are the most common. The lower formu las apply for bends of one degree and they are used for computing the lengths of bends at angles other t han 90 degrees. Multiply the value computed by the actual nu mber of degrees through which the arm of the part is bent.

2. From dimensions given on the part drawing, add the thickness of the stock to the given radius and subtract this from outside dimensions. Fill these in decimally on the sketch 3. Compute the length of arc and write it in the proper position. Note that adding all dimensions gives the over-all length of the part. (See chart in Fig. 18-21.) (For the part under consideration the formula:

A= (

i + R)

1. 5708 is used, as the radius is 2 times

x

the stock thickness .)

18-22. TYPICAL EXAMPLE OF BLANK DEVELOPMENT

18-20. HOLE DIMENSIONS To establish the developed distance to a hole when it is dimensioned from the surface of the bent edge, subtract the sum of the part thickness and the inside ra dius from the given dimension 2, in this case. To this val ue, add the developed radius, taken from the sketch, and the length of the straight arm .

At the upper portion of the illustration is s hown a drawing of a part containing a number of bends. Two sections, a horizontal one marked A - A and a vertical one marked 8 - 8 are taken through the part an d drawn below it. Dimensions are applied directly to th e sections. Horizontal and vertica t dimensions are fo und by addition and subtraction of part drawing dimensions. Dimensions of arcs are found by calculation, usin g the formulas given . After all dim ensions have been applied, the developed flat blank can be easily drawn , as illustrated below the sections. Note that adding al dimensions for both sections gives the length and width of the blank, and a rectangle can be drawn which wi l be the length and width of the finished blank. The drawing is then completed by taking dimensions directly from the sections and the part drawing.

r (\1

+

18-23. FORMED PART DEVELOPMENT Although no more difficult, the development of a formed part requires more steps than one whi ch is simply bent. The difference between bending and for ming basically occurs in the straightness or curvature of the bend line. In bendin g, portions of the blank are raised to some angular position and the line of bend is straight. A forming operation is similar except that th e line is curved instead of strai ght. A formed workpiece is developed by dividing i into sections and finding the length of each secti on

Fig. 18-20. Met hod of determining hole dimension lor deve loped blank.

18-21. FORMULAS FOR BENDS This chart provides all the formulas that you will require for developing corners of bent and formed workpieces . Observe that there are three possible conditions

R

R

T R

T

Inside r adius s rnaller than s tnck thicknes s

R Ins ide radius mor e than twi ce stock thic knes s

R Inside r adius fro m I to 2 times stock thic knes s

--90 o Bends

0

Bends

(4 'T

A•

A-

)

X

+ R

G

+ R)

X

1,5708

.01745

A•

( ~ +R)

A•

(~

A•

xL5708

G

+R)

A ·(~ +R)

+ R) x .01745

Fig. 18-21. Fo rmulas for computing deve loped lengths of bends.

I

X

1, 5708

x .Ol745

OTES

I

2 19

R

-I<£

16-

l..!L

32

PART DRAWING

I

.125

.625

'--..1--1625--t- 147 SECTION

JA-JA

.6875 .147

.875 . 147 2.9375 .122

.375 5.291

. 125 SECT ION

.I 47 1.625

IB-IB

.147

.625 2 .669 DEVELOPED B L ANK

Fig. 18·22. Typi cal example of blank development lor bent port.

by the methods employed for developing a blank for a bent part. Lengths of arcs are determined by employing the formulas given in Fig. 18-21. At A is shown a drawing of a formed workpiece. Wherever the bend occurs in a straight line, it is considered as being bent and wherever the line of bend is curved, it is considered as being formed . Note, however, that any part which contains a form is called a formed part regardless of whether or not it also contains bends . The first step in developing the flat blank is to draw an accurate layout of the top view and front view as shown at B. For small parts, this layout is made to an enlarged scale for increased accuracy . Next, draw evenly spaced lines to divide the formed portions of the part into a convenient number of divisions . Extend the lines so they cross both views. These are actually cutting-plane lines. Sections are to be taken through each. Obviously, the more sections taken the more accurate will be the development. However, this should not be carried to extremes. Large workpieces may require more divisions, while small parts may need fewer divisions to achieve equal accuracy in the development.

On the front view of the layout, draw a line lengthwise to divide the bottom of the part in two. This is shown as line X in the illustration. Now draw the various sections. Observe that the bottoms of the sections are revolved, that is, they are shown as the actual thickness of the part instead of being thicker as cutting-plane lines in the front and top views would appear to indicate. Dimensions are applied directly to the sections in the same way as for ordinary bends . First apply dimensions that can be taken from the part drawing. Then scale the layout for other dimensions. Measure carefully along each cutting-plane line, taking a reading from the top of the part to the bottom where it intersects center line X. In the section views, this is the distance from the top of the section to the center of the horizontal bottom portion. Lengths of arcs are calculated in the same manner as for regular bends. Under each section, enter the various lengths and add them together. These will be developed lengths across the workpiece as measured along each cutting plane line. Now determine linear or length dimensions. The length of line X must be measured because it is the

220

DIMENSIONS AND

.. +

.!.L~ IE

I.L 8

~

3:1

.781 .196 1.312 .196 .781 3 .266

16

4~ 5..!..

•

OTES

l .828

3 R.

32-

.828 .196 1.250 .196 .828 3.298

2

4& A

.'

I

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II

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ur

.

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I

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54 32 I

B

1

1.53 1

1.531

j

. =

IK

r

r

1.343 1.500

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3

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Do S

.968

4

.375 1.343

. 196 .593 .196 1.343 3.671

5

.312

1.500 . 196

. 375 . 196

1.500 3.767

6

1.5 31 .1 96

.3 12 . 19 6 1.53 1 3.76 6

Fig. 18· 23. Typical examp le of blank deve lopmen t for formed part.

same as that of the developed blank as measured along its center line. The next step is to draw the blank layout C, proceeding as follows: Refer to the developed lengths of th e sections and select the longest dimension . On a sheet, draw a center line and two light horizontal lines the same distance apart. This will be the maximum width of the developed blank. On the layout B, measure distance A and on the blank drawing C, apply two vertical lines the same di st ance apart. Next, measure distances B, C, D, etc., and draw vertical lines the same distance s apart on the bl ank drawing. Observe that these dis tances are measured alan g the curve of the part and on line X, view B. In blank layout

C they represent distances along the center line. P rovide yourself with a diemaker's flexible steel sca le. Carefully bend the scale to the contour of the li e before taki ng a reading. Values for arcs may be cal culated instead. When you have finished laying aut vertical gri · lines, mark points on the vertical lines to the res pective dimensions of the sections. Dimensions are marked an equal distance from the center line beca use the blank is s ymmetrical. Several things must be done before an accura e blank layou t can be produced. On another she e: measure the formed portions of the workpiece ala s line Y an d draw th e divisions as shown on the layou:

DIME SIONS AND

OTES

221

r

1

1.500

1.500

T

1

.781

.781

.875 . 406

.312 1.53 1 . 196 .3 12 .19 6 1.531 3 .766

5

4

1.500 .1 96 .406 .196 1.500 3.798

3

1. 187 .196 .875 . 196 1. 187 3 .641

2

r ~---++-+-++-- ---- -

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ii

A

i i ..___ __, ~

. i I

' - - -- - - '

c

BC 0 EF

-

A-

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B C' D E

·i

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Fl

G - HI JK!-- L -

j...-

I'

!

-

-

- -r-

) ...... M

G

H I

JK~ L

E

D Fig. 18·23 (cont.) Typical example of blank deve lopment for formed port.

at 0. The developed layout is then constructed as in E, with the edge distances A,B,C, etc. taken from layout 0, the length of the centerline from C, and respective vertical widths from layout C. This is necessary because the distances A, B, C, etc. along lines Y, which were originally the edges of the blank are not necessarily the same, (in some blanks they may be the same) as A, B, C, etc., measured along line X which is also the center line of the developed blank. Points are connected with a French curve. Observe that the left and right sides are arcs - with large radii instead of straight lines because · of the difference in length of the center line as compared with lengths of the upper and lower edges. The small arcs at the corners are 3/ 16 inch, as taken from the part drawing. Next, the drawing of the developed blank would be fully dimensioned . This drawing is used fo r tracing or laying out the opening in the blanking die. However,

the die opening is not dimensioned on the die drawing. Instead, a print of the blank development is sent to the shop along with the die print. The diemaker will lay out and cut two trial blanks to dimensions given. These will be of the same material and gage thickness as the part drawing specifies for finished workpieces. The forming die is always completed before the blanking die is made and one of the trial blanks would be actually formed in it. Should the formed part be accurate and within the limits established by the part drawing, the diemaker then uses the other trial blank as a template for machining the die hole. Mo re frequently, some modification is necessary because of the way in which the metal flows in forming. The diemaker would then make two more trial blanks, adding or removing stock in an attempt to correct any irregularity. One of these would be formed and checked for accuracy. This process is continued until an accurate blank is produced.

222

DIMENSIO

18·24. DEVELOPING DRAWN PA RTS Before a die for producing a drawn cup or shell can be dimensioned, it is necessary to develop the form, that is, to determine the diameter of the flat blank from which the shell is to be drawn. This dimension must be calculated before the design is begun because the diameter to which the first cu p can be drawn has a direct relationship with the diameter of the flat blank. Also, the blank diameter must be known before the blanking die can be laid out. First, you must realize that blanks for drawn parts cannot be developed in the same manner as blanks for bent or formed wo rk. In drawing, metal is gathered or mo ved from all sides simultaneously and the developed length will be shorter than for corresponding bent or

II

II

OTES

formed workpieces. In the illustration, observe that the developed length of the bent part is 10 inche s, but that the di am eter of a drawn shell having the same pro portions is considerably less. Therefore, for drawn shells, s im ply adding lengths of portions of sections will not provide an accurate dimension for the flat blank . Instead, we must determine the areas of various sections of the shell and co mpare their sum with the area of the fla t blank. The t wo must be equal. There are two methods of determining diameters of flat blank s for drawn shells: 1. They may be calculated mathematically. First the drawn workpiece is separated into its componen t rillgs and disks and the area of each is determined by appropriate fo rmul as 2. Some forms are better developed by a graphical layout. This method is acc urate and relatively fast when it is properly understt\ od. We will now undertak e the study of both methods.

18·25. MATHEMATICAL METHOD

--+--- 4

-----+-'"~"'

~----------1 0 ------------~

BEN DING

t

t

(II

(II

j

I

~----r-

'

t

...

+

/ I

4 9

------~ -,

The fl anged s hell at A is to be drawn to severa l diameters. Divide the shell into flat disks and ringshaped sections . The area of each of these section s must be calculated. Their sum equals the a rea of the developed blank. The diameter of the blank is then fo und in a table of diam eters, ci rcumferences , and areas of circles in a han dbook such as MACHIN ERY'S HANDBOOK, or it may be calculated. (The blank diameter equals the square root of the area multiplied by 1.128) Formulas are given for solving for the areas of each of the nine representative sections. These formul as determine the area of the neutral s urface represented by a line in the center of each section and drawn along it s length. When you are confronted with the problem of deve loping the flat blank for a round shell , first divide it into elementary forms as shown. Then it is a simple matte: to calculate the areas of each. Th eir sum will represen the area of the entire shell at the line drawn along the center of its thickness. The sum will also represen the area of the flat blank if no stretching occu rs . The corresponding diameter is given on the drawing of the of the blanking die followed by the work TRY. The die maker will make a blank by hand and actually try it in the drawing die before beginnin g to build th e blankin _ die.

18-26. BOTTOMS OF SH ELL S When a shell ha s a flat bottom, its division in o component parts is a round, flat disk and the formula for calculating its area was given in the previo illustration. When the bottom is spherical in s hape, different formulas must be employed, depending upothe extent of the spherical surface. This illustratiolists appropriate formu las for use.

18-27. GRAPHICAL METHOD DRAW IN G Fig. 18·24. Different amounts of material are needed lor bending as compared to drawin g.

She lls may be developed graphically, that is , plotting the diameter of the flat blank with line s ins tea:. of computing areas mathematically . The method is c:..:.

DlMENSIO 8 AND NOTE

223

I,

Area :

3.

rro H

5.

rr (D L

- 2R H)

D + E1

6. TTL ( - - ; 2 7,

ri (DL - 2RH )

rT 2 D R

a.

+.L

H/Jj

1

ft~

r- O--j

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2

§\

B. )i

~

uE'Ji·

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a;jA

7

~

3

8

D

r-o----1 ~& §

B.

l'dzf.

rr R2

v-&

0

f y'

r---o-1

- 2

4

Q-

E 0

-o~·

Fig. 18·25. Formu las for solving for non· stretched areas of nine represen tat ive sections of a drawn shel l. I

L

Area = 2 rT

R R2

/ R Ar ea= 2 fT R H

Ar ea = 2 Tr R H Fig. 18·26. Formulas lor solving for areas of spherica l shape.

H

l

224

DIMENSIO S AND NOTE y

t

2

3

3

3

g(f

5 6

7

v

2

v

3

4 .11....------1

I

v

v

3 4

FLANGED SHELL ltl6 (.0625) GA.

6

A T

4

5

v

v

y

5

t

3

?

p

R

6

v

7

v

8

Fig. 18·27. Graphical method for obtaining radi us of developed blank for a she ll .

v

DlfvlENS£0

OTES

application of the theorem of Pappas and Guldinus, which states that the volume of a body generated by revolving a plane section about an axis in the same plane of t he section may be found by the formula: V=

2

77

X

DX A

where: V = Volume of shell D = Distance of the center of gravity of the section from the axis of rotation A = Area of section. The method is relatively simple. Let us apply it to a flanged shell A. Eight steps are taken in developing the blank size, as follows : 1. Draw a section through the left half of the shell and divide it in to its component arcs and straight sec tions as shown. Also draw a longitudinal line along the center of the thickness. Next apply a centerline Y - V at the center of the shell. If the shell is small, draw the section to enlarged scale 2. Number each section. At the right of the view, draw a vertical line and divide it into len gths to correspond with the lengths of the shell sections 1 to 7, measured along the ce nter of the thickness. Solve for lengths of arcs using formulas given in Fig. 18-21, or measure them along the center using a flexib le diemaker's scale 3. Draw lines X and Y, each at an angl e of 45 degrees 4. Extend lines from division points on the vertical line to meet the intersections of lines X and Y as shown, and label them A, B, C, etc. S. Mark the center of gravity of each section of the shell as shown by heavy dots . Note that the center of gravity of rectangular sections is at the enter of each section. The center of gravity of a circular arc is 1/ 3 of arc thickness S, measured from the chord. This is shown as distance T in the inset. Extend vertical lines downward from the center of gravity of each section. Below the section view, draw a line X at the same angle as line X in the diagram at the right 6. Set the protractor to the angle of line A in the diagram. With this setti ng, draw 1a line A below the section view. Locate it from the intersection of line X and the vertical line from section 1, and extend it until i t intersects the vertical line from section 2. Next, set the protractor to the angle of line B in the diagram, and on the section view draw line B from the intersection of line A and section 2 to where it intersects the vertical line from section 3. Continue in this manner until all lines in the diagram have been transfer red to below the section view and drawn to the same angular positions. Next draw line Y and continue it until it intersects line X at J 7. With J as center and with J-0 as radius, draw a circle 0 -H. Then draw a long, horizontal centerline to cross point J 8. Make li ne 0 -P the same length as the vertical line 1 to 7 in the diagram. With the compass point on line H-P, and with the compass set to one-half its length, draw an arc with the left end tangent to circle H-0. The length of the vertical line 0-R is one-half the diameter of the flat blank required for the shell if the section view was drawn actual size.

22 5

18-28. SQUARE AND RECTANGULAR SHELLS Square and rectangular shells are developed by a combination of the methods described for developing bTanks for formed workpieces and for round drawn shells. At the top of the illustration is shown a part drawing for a rectangular drawn shell to be developed to a flat blank. Three s teps are requi red: 1. Sections A - A and B - B are taken through the long and s hort sides of the shell and dimensioned from dimensions given in the pa rt drawing and by employing the formulas given previously 2. Section C - C, taken thro ugh the corner of the shell to the center of the radius, is drawn and developed by the graphical method. Radius 0-R is called the blank radius 3. As shown at A, a rectangle is drawn to represent the length and width of the flat blank. Its l ength equals the sum of all dimensions of the sections A - A, and its wi dth equals the sum of all sections at B - B. Centered within the rectangle is drawn an inverted top view of the finished shell. As shown at B, 45° lines are drawn at the corners to show the corner metal removed. Dimension D is made 0.9375 times the blank radius and it is measured from the center of the corner radius of the finished shell. In other words, multiply length 0-R at Section C - C by 0. 9375 and thi s figure will be dimension D. As shown at C, radii are dra wn at all corners of the flat blank. Radius E of the bl ank is made the same as distance D.

NOTES Notes a re employed to supplement information given by views and dimensions . Individual companies may have one or more special notes that wou ld apply particularly to the products they manufacture. In your first day in any job, you should be ve ry observant to determine what special methods are follow ed. In a large plant you will be supplied wit h a standards book. Study t his carefully for special ways of preparing drawings. In smaller plants you would do well to study a few of their drawings or blueprints. In addition to conventional notes which apply for tool drawings, die drawings us ually have one or more special notes that apply for dies only.

IDENTIFYING CALCULATED DIMENSIONS There are thr ee ways of i den tifying calcu lated dimensions on drawings. Above the dimension line, and immediately following the dimension, may be lettered one of the followi ng: 1. TRY 2. DEV. (Develop) 3. APPROX. (Approximate) Select the one in use in the plant for which the die is being designed. Where there is no particular preference, I always use 'TRY ' because it describes better what is actually to be accomplished. An y of the foregoing indicates to the die maker th at he is to make a sample blank and actually bend, form , or draw the metal to make sure that dimensions of the formed part are within limits established by the part drawing.

226

,/

IB

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A

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~IB

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A

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__________ ____ _

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RECTANGULAR SHELL :11: 16 GA . (.0625)

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.Sit5

.8125

' -~

+

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~

+

+

l

+

+

l

'-----------------"'

B

2.750

SECTI O N

fA. - JA. y

/ - -- ------- - --- - -- -~ ,

I I

f

.8125

t

t

I I

I I I

.8125

I I I

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(

I +

t

,_

S ECTIO N

IB - IB

v SECTI O N

(C - (C

I I

, 1

c

E

Fig. 18·28. Method of develop ing o blank for a re ctangular shell.

18-29. TOOL IDENTIFICATION NOTE This not e give s the tool number and it directs that it is to be stamped or marked on the die. In addition, it shows the appro ximate location in which it is to be placed. The note is written by lettering the word, 'STAMP' or 'MARK', and appl yi ng the tool number directly underneath . A leade r points to the finished pad on the die set where the note is to be applied.

18-30. HARDEN AND GRIND NOTE On assembly drawings, the fact that a component is to be hardened and ground is indicated by applying the

abbreviation H . & G. above the leader of the det a1: number as at A. When a part is detailed individu al.'· the abbreviation H. & G. is lettered immediately fo llow· the part and material. It is applied under the vie ws of the detail drawing, as shown at 8 .

WOR K TO PART PRINT This note is applied to drawings which do not co::· tain dimen s ions for those portions of the punches aac die blocks which pertain to the blank or workpiece. T:-:e note inform s the die maker that he is to obt ain a:. such dim ensions directly from the .part print.

OTES

227

@ DIE

BLOCK- TS -H.II:G.-1 REQ'D

B Fig. 18-30. Manner in which o harden and gr ind note is placed on on assembly drawing (A) and below the views of a detai l drawing (B). STAMP

TD-107687

Fig. 18-29. Manner in which c too l number note is placed on a drawing.

NO ALLOWAN CE HAS BEEN MADE FOR SPRINGBACK This note is lettered on most bending and forming dies and it informs the die maker that spring-back cannot be tolerated in the workpiece. After the die has been built, he is to try it out and make app ropriate corrections. Spring-back varies between 1/ 4 degree and 2 degrees and it is the amount that a bent or formed portion of a workpiece deflects backward after bending or forming. For some parts, spring-back may not be objectionable and the note is then omitted.

DIE MUST PRODUCE PA RT TO PRINT This note is applied to drawings of dies which are to form a complete part. rt is a clear indication to the die maker that he is to try out the die after it has been built and apply all necessary adjustments so that workpieces will meet tolerances indicated on the part print.

WORK TO TEMPLA TE

...

When contours of a part are very irregular, this note may be applied on the drawing and a leader is added to indicate the contour against which a template is to be used for checking. Dimensions for making the template are ordinarily taken directly from the part drawing. A template is made from sheet steel. Lines are scribed accurately to given dimensions and unwanted portions are then cut away. As work progresses, components are checked against the template until contours match perfectly.

DEVELOP BLANK This note may be applied on layouts of bending, forming, or drawing dies, or a calculated dimension

may be given followed by the work 1 TRY' as previously explained. Both have the same meaning. The bending, forming, or drawing die is to be made first before the blanking die is built. Sample blanks are to be cut by hand and formed to establish final dimensions of the blanking die opening.

ALLOWFOR TRIMMI NG OPERAT ION This note is applied on layouts of drawing dies and it means that sufficient material is to be provided for a trimming operation to follow the drawing or forming operation. After blank development, this allowance is added for determining final dimensions of the blanking die opening.

SHAVE ENTIRE CONT OUR This note specifies that a shaving die is to be designed in addition to a blanking die and that suitable extra material must be allowed for the shaving operation.

READING A PART DRA WING From the foregoing it should be apparent that in reading a part drawing the die designer must pay particular attention to notes because many of them, even short ones, are important far in excess of the amount of space they occupy. For instance, the note MUST BE FLAT on a drawing often means that a compound die must be designed instead of a progressive die which might be decided upon if the note were absent. The note MUST BE SQUARE applied to the edge of a drawn or formed workpiece means that the edge must be trimmed in a trimming die or by some other means and that material must be provided for this operation. Therefore, all notes should be considered analytically before a design decision is made.

Section 19

THE BILL OF MATERIAL Considerable background knowledge is necessary for listing information in the bill of material because it is precisely then that final determination is made of the materials from which the various die members are to be constructed. These decisions wi ll influence success or failure of the completed die in operation. In addition, the desi gner must know the names of the various components that make up the die and he must know which materials ha ve proved successful for similar members in previous work . Also, he must be familiar with standard and purchased components, the sizes in which they are available, and the conventional methods of listing them. Filling in the bill of material column, therefore, is an important element in the preparation of a die drawing and a die designer must become proficient at it.

COt-ITEt-ITS The bill of material is a list of the followi ng: 1. Rough sizes of blocks of steel or other materia ls that will be required fo r making special components of the die 2. Standard parts which are to be taken from stock 3. Parts to be purchased specifically fo r the job. These are standard components that are not ordinarily carried in stock. The bill of material, then, is a complete list of every component in the tool or die .

19-1 . DIE ORA Wi t-I G The final step in preparing a die drawing is to fill in the bill of material column. On drawings for many die shops, the bill of material is placed at the upper right corner and it is read downward as shown. For others, it is located at the lower right corner and it is read upward. The bill of material is divided into five columns, usually . When extending the printed lines to complete columns, draw them exactly the same width. If the sheet

228

has one or two horizontal lines printed for the first details, make all succeeding boxes the same height. When the sheet does not have starting lines, space horizontal lines 5/ 16 inch apart. First extend the left vertical line i!l'ld mark 5/ 16 inch spaces along its length with small dividers. Then draw horizontal lines, and complete the columns by extending vertical lines. Draw as many horizontal lines as there are detai l numbers in the assembly, and no more. In the fi rst column marked DET., the abbreviation for detail, write detail numbers, beginnin g with number one and continuing for the total number of details in the assembly. The second column is marked REQ'D, the abbreviation for required. This lists the numbe r of parts needed for each detail number. Fi ll in these amounts very carefully because it is easy to miss parts that do not show in every view. The third column marked PART NAME lists the name of each component. Learning names of parts is just as important as learning to draw them . They form an important portion of the language of the die designer which you are now learning to understand. In the fourth column , MAT., are listed the materials from which the parts are to be made. For parts avai lable commercially, this space indicates whether they are to be purchased or are available from stock. In the final column. SPECIFICA TIONS, stock sizes are listed, as well as catalo numbers of purchased items. There are two methods of specifying stock for special parts: 1. An allowance is applied for machining whereve it is required 2. All parts are listed exact size, and the stock cutter applies extra stock where it is required for machining. About three-quarters of all plants use the first method, and the remaining quarter use the second method. Note, however, that when exact sizes are given, (method number 2), a note is usually printed to that effect near the bill of material column .

~ t'j to &

7is

<; i!

~ t:"" t-< 0

2.

":::j

.

-3

5""'5 --- - -- -----:

PU NIC. ~

.5

2

I&.ANK. IP IL.OT

6

2

I FI' ILOT NU T

I

7 e 9

:::::

> >-3

SOC.. 5tT SC.f'. .

t'j

1:0

•0

> t""'

2.

II

12 1.3 I

1

I S.PA..ING PIH

14 I

I

I ~ !>PIY N G

1.5 I 16 I

I I

!A UTO STOP l f'RONT S,f'll([f\

6 6

150C. etJTTl(IO SOC. CAP ~(R .

6

IOOW[L 00 W£L

J1 ~&

I

191 20

6

2 I I .. !OOWEL 2 21 & I >OC~ APS£ R_ 2 3 I I !S T RIP REST 2"'- I 1 I !!>At " &A u~ Z~

I

I

IFINGU\ HO P

2 b I

I

l HI NG[ PI N

NOT[ : C.l E.C..RANC[ PE..R. SfOE. 00 2

0Q.4NLV Ql!: >tT CAT ~

Ot!O& · AI 5 T CfL S Hl O

e.u'H

I~

QIA S HAN K ~i GUt O€ PO)TS

OA . C.'50Rt f. T AP ~l!; -18 SOC. l-ID C. AP S(.R

~

ti R ~tt~ . TI-IR.U · 8F; ~

.S ECT IO N

fA. - fA. P Uf'£.H t.C.L AN .C:

.

'"'

"

.

F .) F\ ~

M_Q_Pf'E,~

>< 066

..5· 23 - 6 1 P A.OUIN

Fig. 19-1. Bill of material is shown in upper right hand c:orner of th i s di e drawing.


NO.

31 tv tv

<0

230

THE BILL OF MA TERIAL

19-2. TYPES OF COMPONENTS

1. Die Block

Referring once again to the representative die which has formed the basis for these studies, we find that eleven types of components are to be listed in the bill of material, as follows:

2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Blankin g Punch Piercing Punch Punch Plate Pilot Back Gage Finger stop Autom atic Stop Stripper Fasteners Die Set.

Each of these classifications would have other die components associated with it by function. Illustrations to follow will show exactly how each of the eleven basic components should be listed , In addition , listings for related die parts are included so your understanding will be complete.

19-3. DIE BLOCK

- --®

This shows how the first component, the die block, is listed in the bill of material. In addition the representative bill of material lists those members which could properly be associated or identified with the die block . Observe that many words are abbreviated and compare the abbreviations with the following list which corresponds to the illustrated list: 1. DIE BLOCK 2. DIE SECTION 3. INSERT 4. COMPOSITE SECTION 5. DIE BUTTON 6. FORMING BLOCK 7. DRAWING RING 8. HORN 9. SPACER.

---{D

CET.

Fig . 19·2. Types of components that ore listed in the bi ll of mote· rial.

REQ'O

PART NAME

MAT.

SPECIFICAT IONS

I

I

DIE BLOCK

2

4

DIE SECTION

bHTS I 1;4 X 4 X 4 5;8 TS. 11/4 X 3 X 5

3

2

INSERT

H.CHC 1;2 X I X 11/4

4

6

COMP. SECT

PUR. SEE NOTE

5

4

DIE BUTT'N

6 7

I I

FORM. BLOCK DRAW. RING

T.S \ 11/40 IA. XII/2 TS. '1112 X 3 X 5 1/4

8 9

I

2

HORN SPACER

8 DIA. X 2 1/2 T.S. 3 DIA. X 6 1/4 M .S . :.3;4 X 4 X 7 T.S.

Fig. 19-3. How die block members are listed in the bill of mole ri o

231

TIIE BILL OF MATERIAL

19-4. BLANKING PUNCH The punch produces a blank or portion of a blank, and it is the male member or component of any die. The punch is positioned above the die block in all but a few types of inverted dies. It derives its nnme from the type of die in which it is applied. The punch of a blanking die is called a b lanking punch. The punch of a t rimming die is called a trimming punch, etc . Following a re listed seventeen types of punches to correspond with seventeen types of dies. In the illustration , note carefully how the names of punches are abbreviated in the bill of material column. 1. BLANKING PUNCH 2. CUT OFF PUNCH 3. TRIMMING PUNCH 4. SHAVING PUNCH 5. BROACHING PUNCH 6. BENDING PUNCH 7. FORMING PUNCH 8. DRA WING PUNCH 9. CURLING PUNCH 10. EXTRUDING PUNCH 11. SWAGING PUNCH

12 . PARTING PUNCH 13. NOTCHING PUNCH 14. LANCING PUNCH

15. STAKING PUNCH 16. COINING PUNCH 17. BUl
OET.

REQ ·O

PART NAME

MAT.

SPEC I FICATIONS

I

2

PIERCE. PUNCH TS.

3/4 DIA . X J3;4

2

4

PERF. PUNCH

D.R.

3/32 DIA. X I 5t8

3

I

H'lC UT PUNCH T.S.

3 1/4 D IA. X 13; 4

4

I

C'SINK PUNCH

5

2

QUILL

6

I

KEY

T.S. 112 OIA. X 13/4 TS. 3/4 DIA. X 13/ 4 M.S. 1/ 4 X 1;2 X I

Fig. 19-5. How piercing punches and their associated componenls ore listed in o bill of maleriol.

19-6. PUNCH PLATE CET.

REQ 'C

PAR T NAME

MAT.

SPECIFICATIONS

I

I

BLANK. PUNCH PHT.S I 3/4 X 3 X 4 IJ2

2

I

C'OFF PUNCH

T.S. 13/4 X 4 X 6

3

I

TR IM PUNCH

T.S. 81;2 DIA.X 2

4

I

SHAVE. PUNCH

TS.

5

I

--

BROACH.PUNCH

TS.

I

BEND. PUNCH

13/4 X 2 X 3 TS. 3 X 4 1/2 X 5

7

I

FORM PUNCH

TS.

2 X 4 X 6 3;4

8

I

DRAW. PUNCH

TS.

9 DIA. X 3

9

I

CURL. PUNCH

TS . 10 DIA . X 4 1;4 TS. 1112 DIA. X 2 T.S. I DIA . X 2 1/e

6

--- -- -

--

6 DIA. X I 3/4

_J

EXTR. PUNCH • .w- . -

II

I

SWAGE. PUNCH

12

I

PART. PUNCH

13

I

NOTCH. PUNCH

14

I

15

2

16

I

LANCE. PUNCH T.S. I DIA. X 3 STAKE. PUNCH TS. 3t4 X I X I 3/4 CO IN. PUNCH H.S.S. 1112 D IA. X 2

17

I

BURN. PUNCH

~

- --

A punch plate is a plate or block used to retain piercing punches. A simple square plate may retain a

T.S. 1112 X 3 X 7 T.S 13/4 X 2 X 3

T.S.

3 DIA. X 3 3te

Fig. 19-4. Seventeen types of punc hes ond how each would be listed on a bil l of mater ial.

DET.

REQ'O

I

I

PUNCH PLATE M.S. 3/4 X 8 X 10

2 3

I

BACK. PLATE

I

SPACER

PART NAME

MAT.

T.S.

SPECIFICATIONS

l/4 X 3 X 4l;4

CRS. I X 4 X 6 112

Fig. 19·6. How a punch plate, backing plate and spacer ore listed in a bil l of materia l.

232

THE BILL OF MATERIAL

single punch, wh1le a large punch plate may contain hundreds of precision-bored boles for retaining a corresponding numb er of piercing punches. As the followin g list indicates, backing plates and spacers are closely associated with punch plates.

1. PUNCH PLATE 2. BACKING PLATE 3. SPACER.

19-7. PILOTS Pilots provide a method of accurate location of the strip. Associated with a pilot would be its pilot nut and in one type of spring-backed pilot, one or more detents. A locating plug, or locating pin and diamond pin, would perform the same function of precision location fo r some types of secondary-operation dies. Following is a list of details related to the pilot:

PILOT PILOT NU T DETENT LOCATING PLUG LOCATING PIN DIAMOND PIN.

1. 2. 3. 4. S. 6.

DET. REO'D

P"RT N"ME

I

2

PILOT

2

2

PILOT NUT

3

I

4

5 6

19-8. BACK GAGE In its travel through the die, th e strip is positioned against the back gage. Associated with the back gage is the front spacer and strip s upport. When the s trip must be centered, an equalizing device is designed for positi oning it exactly over the center of the die hole. For s econdary operations, gages or nests are employed for locating the workpieces. Here is a list of details relat ed to lhe back gage: 1. BACK GAGE

2. 3. 4. 5. 6.

FRONT SPACER STRIP SUPPORT EQUALIZING BAR GAGE NEST.

19-9. FINGER STOP The fin ge r stop positions the strip for the first stroke or operation . Related to it would be the stock pusher which keeps the strip registered against the back gage. Some finger stops serve the dua l purposes of stop and stock pusher . A stop block is used in cut off dies. 1. FINGER STOP

2. STOCK PUSHER 3. STOP BLOCK

M ... T.

SPEC IFIC" TIONS

T S . 3;8 D IA . X I 3;4 CHS

lf2 DIA. X I

DETENT

D.R. 31t6 DIA. X 3;8

I

LOC. PLUG

TS.

I

LOC . P I N

I

DIAMOND PIN

1112 DIA. X 41;8 5;8 DIA . X I 5;8 TS. TS. 5;8 OIA. X 15;8

Fig. 19·7. How pilot details are listed in a bi ll of material.

DET. REO·O

I

I

2

I

PART NAME

CET. REOC

PART NAME

MAT .

SPECIFICATIONS

C.RS 1;8 X 3;8 X I 7; 8

I

I

FINGER STOP

2

I

STOCK PUSH .

TS. IJs X 5;8 X 2

3

I

STOP BLOCK

TS . I 1; 2 X 2 X 2 1/ e

Fig. 19·9. How a linger stop, stock pusher and stop block are Ii sled in a bi II of materia l.

MAT.

SPECIFICATIONS

TS . t; 8 x 1 x 8 FRONT SPACER CR.S l;9 X I X S l/4 STRIP SUPPORT CRS 1; 8 x 11;4 x 3 CRS 114 X I X 5 EQUAL. BAR BACK GAGE

3

I

4

I

5

2

GAGE

T.S. 1;4 X I 3;4 X 3

6

I

NEST

T.S.l 1/4 X 4 X 61;2

Fig. 19-8. How detai ls rela ted to the back gage ore li sted in the bill of materia l.


233

19-10. AUTOMATIC STOP Dies designed for hand feeding of strip are provided with an automatic stop. Large blanking dies, run in s low moving presses, are provided with a stop pin instead. Six parts are included in the conventional automatic stop assembly: 1. AUTOMATIC STOP 2. FULCRUM PIN 3. SPRING PIN 4. SPRING S. SQUARE-HEAD SET SCREW 6. JAM NUT 7. STOP PIN.

~ DET.

F!EQ·O

~ J'cD P"F!T NAME

MAT.

SPECIFICATIONS

2

FULCRUM PIN

T.S. 1t4 X 1te X 4 D.R. 1;8 DIA. X 3

3

SPRING PIN

CR.S 114 DIA. X 3 1/4

4

SPRING

5

SQ.HD.SET SCR. STD. 1/4-20 X 2 1/4 JAM NUT STD. 114- 20 STOP PIN O.R. 1/4 DIA . X 2

I

AUTO. STOP

6

7

s.w.

by listing the diameter of the engaging bolt. Sizes of rivets are given by listing the diameter followed by length. Compare the following list with the abbreviations in the illustration: 1. SOCKET CAP SC EW 2. SOCKET SET SCREW 3. SOCKET LOCK SCREW 4. SOCKET BUTTON HEAD SCREW 5. SOCKET FLAT HEAD SCREW 6. STRIPPER BOLT 7. DOWEL 8. HEXAGON NUT 9. JAM NUT 10. WASHER 11. RIVET- FLAT HEAD.

TO

SUIT

Fig. 19·10. How parts of on automatic stop assemb ly and a stop pin ore lis ted in o bill of material.

19-11. STRIPPER PLATE A stripper, whether of the solid type or the springoperated variety, is the die member that strips or removes the material from around punches . Associated in function with it are ejectors, knockouts , and their accessories, as shown by the following list: 1. STRIPPER PLATE 2. BLANK HOLDER 3. PRESSURE PAD 4. EJECTOR 5. KNOCKOUT PLATE 6. KNOCKOUT BLOCK 7. KNOCKOUT COLLAR 8. K OCKOUT ROD 9. PRESSURE PIN 10. GUIDE PIN 11. GUIDE BUSHING 12. DIE SPRING. 19-12. FASTENERS This shows the method of listing the mos t frequently used types of fasteners. Observe that fasteners are marked STD. , or Standard, in the Material column. This means that they are carried in stock. In the Specifications column, screw sizes are noted by giving the diameter, followed by the number of th reads per inch, and the length. St ripper bolt sizes are noted by giving the body diameter, followed by the len gth from under the head to the shoulder. Dowels are listed by giving the diameter followed by length. Sizes of nuts are given by listing the diameter of the engaging bolt and the num ber of threads per inch. Sizes of washers are given

~: ~

c = ~~:~

~\.'"-~ I

DET.

REQ·O

P"RT NAM E

MAT.

SPEC I FICATIONS

I

isTRIP. PLATE

M.S . lf2 X 6 X 8

2

BLANK HOLD.

TS . 3/4 X 8 1/ 2 X 10

3

PRESS. PAD

TS.

4

EJECTOR

TS. 3/4 X J3/4 X 3 M.S 3'12 DIA. X 5; 8

I X 2 1/2 X 4

5

KN'OUT PLATE

6

KN'OUT BLOCK M.S.

7

KN'OUT COLLAR CR.S I" DIA . X 3/4 KN'OUT ROD CR.S lf2 DIA. X 7 3;16

8

4 DIA. X 3 lt 8

9

2

PRESS. PI N

10

2

GU IDE P IN

II

2

GUIDE BUSH.

CR.S. lt4 DIA. X 2 lt 8 D.R. 1!2 DIA. X 4 l/4 TS . I" DIA. X 71

12

4

"STD" SPRING

PUR. #QS-YH- 10

8

Fig. 19-11. Howthe stri pper and details associated with it are shown in o bi II of ma terial.

OET . REQ'O

I

4

2

2

3

2

4 5

4

PART NAME

MAT.

SPECIF'ICATIONS

SOC.CAP SCR. STD. 3t8 -16 x2 1t 4 SOC.SET SCR. STD. lf:2· 13X 3/4 SOC.LOCK SCR. STD. 112·13 X 1/ 4 SOC. BT T N HD. STD. St16 -1 8 x 1 112

7

2

SOC.FL.HO. SCR STD. 3;8 ·16 X 2 STRIPPER BOLT STD. 1;2 OIA. X 2 112 DOWEL STD. 3;8 DIA. X 1112

8

4

HEX . NUT

STD.

9

4

JAM N UT

STD.

10

2

WASHER

II

4

6

2 4

112- 13 3/a-16

1/2 DIA. STD. RIVET- FL . HD. STD. 1/4 DIA. X 112

Fig. 19- 12. Lis ti ng fa steners in a bill of mater ial.

234


19-13. DIE SET There is usually not enough room to list all the die set information required. The reader of the drawin g is therefore directed to a note on the drawing itself in which specifications of the die set and its component parts are given . In some types of dies , a side cam or scrap cutter may be fastened to the die set and these are li s ted here. Both are usually made of waterhardening tool steel, given si mply as the abbreviation, T.S. 1. DI E SET 2. SIDE CAM 3. SCRAP CUTTER,

DET. REQ·O

PART NAME

MAT .

SPECIF ICATIONS

I

I

DI E S ET

PU R. SEE NO T E

2 3

2

SID E CAM

T.S . 2 X 3 1/2 X 7

I

SCRAP CUT.

TS.

13/4 X 2 1/2X3

Fig. 19·13. How the die set, side com and scrap cutter are listed in a bil l of materia l.

COLUMNS Let us now consider the main divisions of information contained in the bill of material. As shown in previous i llustrations, the bill of material is divided into fiv e columns: 1. DET. (Detail) 2. REQ'D (Requi red) 3. PART NAME 4. MAT . ( aterial) S. SPECIFIC ATIONS.

3. Purchased as semblies, although composed of several parts, are given a single detail number. 4. We ldments are given a single detail number .

NUMBER REQUIRED (Colu mn 2) Before specifying the number required, study all the vie ws to determin e exactly how many of the particular componen t a re requi red. In many cases a single view will not show the total number and other views must be considered as we ll.

PART NAME (Column 3) In listing the name of a part, give the general name first , followed by any word or abbreviation qualifying it. For example, a right-hand V block would be listed as V BLOCK - R.H. Note th at t he name, V Block, is listed first, followed by the abbrevia tion for Ri ghtHand because the 'hand' qualifies or limits the ty pe of V Block that is specified. It is frequently necessary to shorten the part name because of the limited space available. For instance, when specifying a key, we may turn to the Lodding catalog and find a suitable one listed as Plain Fixture Key. In addition to this rather long name, we must add the work Loddi ng, which makes the pa rt name entirely too long for the space provided. The name is better shortened to LODDIN G KEY. This is sufficient ide ntification when given in conjunction with t he catalog number listed i n the SPECIFICATIONS column.

19-1.4. MATERIAL (Co lumn 4) In the material column is l isted the material from which the component is to be made. Th e name of the materia l is usually abbreviated beca use of lim ite d space . For dies, t he most commonly employed materials a re tool steel and machine steel. Blanks for making cutti ng members of dies are sawed from bars of tool steel. At least 1/ 8 inch of material should be allowed per side for machinin g. This is measured fro m the outside of the bar to fina l size. Sha ding i n the illustration shows th e depth of this layer of decarburized s teel and iron oxide, or scale. If not removed pre viou sly, the ha rd ening operation would le ave soft spots and produce surface cracks .

DETAIL NUMBER (Column 1) The first column, DET., lists numbe rs that have assigned to the components of th e die. Obse rve these rules: 1. One number identifies all identical parts . For example, all 5/ 16 dia . by 1 1/4 inch long dowe ls would have the s ame number. It is lettered only once on the drawing, enclosed within a detail circle, and with a leader pointing to one of the components. 2. All parts that are different, however slightly, from other parts are given individual numbers. For exa mple, a 1/4 dia . by 1 inch long dowel would have one number, while a 1/ 4 dia. by 1 1/4 inch long dowel would be given a different num ber.

Fig. 19· 14. Shaded areas of these too l steel bar s den ote outsi de laye r of decarburi zed steel, iron oxide, or sca le and ore removed b machining in mak ing cutting membe rs of dies.

19-15. DIRECTION OF GRAIN Blanks fo r making punches and small die blocks are preferably cut with the gra1n of steel at right angles to cuttin g faces to reduce hardening distortion. In the

235

THE BILL OF MATERIAL illustration, the grain runs in the direction of the parallel lines, always along the length of steel ba rs . Cutting faces A will be at ri ght angles to the grain in finished punches . Of course, positioning cutting faces across the grain is pos sible onl y fo r small cOJllponents within commercial tool steel sizes .

1-ig. 19-15. Di rection of gra' n is pa ralle l to the axes of thes e steel bar s and is at ri ght angles to the cut ti ng face s of punches made ther efrom .

19-16. LARGE CUTTING MEMBERS When ordering tool s teel for large die blocks , consider th at distortion is greatest length wise with grain directi on and s tock shou ld be ordered so distortion will be kept to a minimum. Die hol e contour will gove rn the decision. The rule is: P lace the longest dimension of a narrow die hole opening across the grain. Distortion in the slot at A will be more exten sive tha n if it is l ocated across the grain as at B. This me ans that swelling or sh rinkin g distortion will shorten or lengthen the s lot at A more than it would be affected if posi tioned across the grain as at B.

~

R

F

--

A

......... 8

Fig. 19-16. Less dis tortion wi II be expe rienced iI longest dimens ion of die hole is pos it ioned across the grain as at (B).

19-17. AVOIDING CRACKS IN HARDENING Cracks tend to occur along the grain of the material. When sharp corners are present in the die hole, order the stock so the grain will be across t he corners as at A, and not in line with them as at B. Sharp corn e rs provide a focal point for fractures and correct app lic-

B A

~ 8

Fig. 19·17. Si nce crocks tend to occur along the groi n of the ma ter ial , bes t pos it ion of die ho le with sha rp corners is shown at (A).

ation of grain direction will help to eliminate this source of trouble.

TOOL STEELS Tool steel is specified for numerous die components and it may be well to discuss briefly the most commonly used types. They are: 1. Water Hardening Tool Steel 2 . Oil Hardening Tool Steel 3. Air Hardening Tool Steel 4. High Carbon-High Chromium Tool Steel 5. High Speed Steel 6. Shock Resisting Tool Steel 7. Hot Work Die Steel. 1. Water Hardening Tool Steel As its name indicates, water hardening tool s teel is hardened by quenching it in water after it has first been heated to proper hardening temperature. It is employed for parts which c an be groun d after ha rdenin g. Water hardenin g tool steel is subject to distortion in the hardening process and it should not be specified for parts with internal contours that must remain accurate and which cannot be ground after ha rden in g. 2. Oiling Hardening Tool Steel Oil hardening tool steel con tains chrom ium and it is quenched in oil in the ha rden ing process. Warpage or distortion is much less than for corresponding grades of water hardenin g steels. When accurate surfaces cannot be ground a fter hardenin g, and an ticipated production rates a re average, oil ha rdening tool steel should be specified. The abbreviati on is O.H. T. S. 3. Air Harden ing Tool Steel Air hardening tool steel need not be quenched in either oil or water for hardenin g to occur. After heating beyond the c ritical range, it is simply exposed in air until cool. Air hardening tool steels have minimum warpage and this is combined with greate r tough nes s and wear resistance than correspondi ng grades of oi l or water hardenin g steels . 4. Hi gh Carbon, High Chromium Tool Steel High carbon, high chromium steels have a bout the same pro pe rties as air hardenin g steels except that the y posses a greater degree of resistance to wear. High carbon-high chromium steels should be specified for die parts when long production run s are anticipated. 5. Hi gh Speed Steel The outstanding quality of high speed steel is its toughness, combined with a high degree of wear resistance. It should be specified for weak di e parts such as frail inserts, small diameter punches, and the like. Another excellent application is in dies for cold working, coining and upse ttin g of metal. 6. Shock Resisting Tool Steel Stock res istin g tool steel contains a smaller amount of carbon and therefore it is tougher than other types. It is employed for heavy cutting and forming operat i ons where steels with a highe r carbon content would be subject to breakage. 7. Hot Work Die Steel These steels a re employed in dies designed for forming hot mat erials because they possess high resistance to softening under heat.

236


TYPE OF STEEL

Non Deform ing Properties

Salety in Hardening

Tough ness

Wear Resistance

Ma.c hineabllity

Res istan ce to Softening Under Heat

WATER HARDENING TOOL STEEL

POOR

FAIR

GOOD

FAIR

BEST

POOR

OIL HARDENING TOOL STEEL

GOOD

GOOD

FAIR

FAIR

GOOD

POOR

AIR HARDENING TOOL STEE L

BEST

BEST

FAIR

GOOD

FAIR

FAIR

HIGH CARBON HIGH CHROME

BEST

BES T

POOR

BEST

POOR

FAIR

HIGH-SPEED STEEL

GOOD

BEST

BEST

GOOD

FAIR

GOOD

SHOCK RESISTING TOOL STEE L

FAIR

GOOD

BEST

FAIR

FAIR

FAIR

HOT WORK DIE STEEL

BEST

BEST

BEST

F AIR

FAIR

GOOD

.....

Fig . 19-18. Guide for the proper selection of tool steel.

19-18. PROPERTIES OF TOOL STEELS

MEDIUM CARBON STEELS, S.A .E. 1033 to 1052

Thi s chart provides a gui de for the selection of the proper tool steel fo r any given application. Ob serve that seven types are listed in the first column. In the second column is given the non-deforming property fo r each type. This is an i mportant factor for many die blocks and punches. Othe r important properties are given in succeedi ng columns to aid in selecting the type of tool steel having exactly the properties desired.

These are sometimes called low carbon tool steels . They can be ha rdened a certain amount by heating and quenching in oil. For examp le, S.A.E. 1040 will harden to about Rockwell C-45. They mac hine readily and they can be welded if allowed to cool slowly to avoid cracking.

S.A.E . NUMBERING SYSTEM The S.A.E. system of numbering steel was ori gina ted by the Society of Automotive Engineers and it is wi dely used. You should be familiar with the system because the materi al of many stampings, as gi ven on part drawings, is often specified by S.A.E. number. Following is a bri ef summary :

HIGH CARBON STEELS, S.A.E. 1055 to 1095 High carbon steels go under the general name tool steel and they are specified when good wear characteris tics are requi red. When purchased, tool steels are in the soft state and they machin e fairly well. Hardening is accomplished by heating and quenching. After hardening, any fu rther machining must be acc omplished by gri nding. Tool steel should not be welded.

SPECIFICATIONS (Column 5) LOW CARBON STEELS, S.A.E. 1006 to 1015 This group of s teels weld readily, but they do not machine freely, especially when smooth su rfaces are req uired .

LOW CARBON STEELS, S.A.E . 1016 to 1030 This group of low carbon stee ls gene rally go under th e general name of machine s teel. They can be readily welded, easily machined, and ha ve sufficient strength fo r most tooling applications . When hard surfaces are required, they may be cas e-hardened, either by carburizing or by cyaniding.

The final step in filling in the bill of material is to gi ve the specifications of the variou s componen ts . For square and rectangular bars, this consists o giving the thickness , width, and length . For roun d bars, the diamete r is given, followed by the length. Standard pa rts such as fasteners are listed by givin g the dia meter, followed by the number of threads per inch and the length. For purchased components, th e catalog number is given. For small sprin gs, the no e TO SUIT is applied . When there is not enou gh space o list the sp ecifications, the wo rds SEE NOTE are lettered in the box in the bill of ma terial and speci fications are given in a note on the drawing.

Section 20

TYPES OF DIES In previous sections of this book, you have learned the elements that go into building a complete die. In addition, you have lea rned how to design a die, that is, how to arrange those elements - the die block, punches, stops, gages, die set, and all the others into a functioning die. Also, the preparation of a die drawing was explained in detail so your comprehension would be a thorough one. The next step is to learn about the types of dies, their function, and how they operate. There are twenty types of dies and each is distinct and different from all the other types. However, as you study the descriptions to follow, observe how the elements that you learned previously are applied and reapplied with

suitable modifications to adapt them for each particular job to be performed.

20- 1.

BL A ~Kl ~G DIE S

A blanking die produces a blank by cutting the entire periphery in one simultaneous operation. Three advantages are realized when a part is blanked: ' 1. Accuracy. The edges of blanked parts are accurate in relation to each other 2. Appearance. The burnished edge of each blank extends around its entire periphery on the same side. 3. Flatness. Blanked parts are flat because of the even compression of material between punch and die cutting edges. The inset at A shows a material strip ready to be run through a blanking die. At B is shown the top view of the die with punches removed. The section view at C shows the die in open position with the upper punch raised to allow advance of the strip against the automatic stop. At 0 the die is shown closed with a blank pushed out of the strip. Blanking dies may produce plain blanks as shown in inset E, but more frequently holes are pierced at one station and the part is then blanked out at the second station . Such dies are called "pierce and blank" dies and they have been described fully in preceding sections of the book .

B

0

c Fig . 20-1. Blanking die.

237

238

TYPES OF DIES

20-2. CUT OFF DIES The basic operation of a cut off die consists in severing strips into short lengths to produce blanks. The line of cut may be straight or curved, and holes or notches or both may be applied in previous operations. Cut off dies are used for producing blanks having straight, parallel sides because they are less expensive to build than blank in g dies . In operation, the material strip A is registered against stop block B. Descent of the upper die causes the cut off punch C to separate the blank from the stri p. Stop block B also guides the punch while cutting occurs to prevent deflection and excessive wear on guide posts and bushings. A conventional solid stripper is employed.

Fig. 20·2 . Cut off die.

20-3. COMPOU ND DIES In a com pound die, holes are pierced at the same station as the part is blanked, instead of at a previous station as is done in a pierce and blank die. The result is greater accuracy in the blank. Whatever accuracy is "built in" the die will be duplicated in every blank produced by it.

Fig. 20-3. Compound die .

239

TYPES OF DIES Compound dies a re inverted dies. The blanking punch A is located on the die holder of the die set instead of being fastened to the punch holder as in conventional dies, and it is provided with tapered holes for disposal of slugs . The die block B is fastened to the punch holder and it is backed up by a spacer C which retains piercing punches. A positive knockout removes the blank from within the die cavity near the top of the press stroke. A spring stripper removes the material strip from around the blanking punch. Although most compound dies are designed for producing accurate, flat blanks, they are occasionally used for producing blanks that are too large for production in more than one station. Si nce all operations are performed at the same station, compound dies are very compact and a smaller die set can be applied.

20-·4. TRIMMING DIES Trimming dies cut away portions of formed or drawn workpieces that have become wavy and irregular. This condition occurs because of uneven flow of metal during forming operations. Trimming removes this unwanted portion to produce square edges and accurate con tours. The illustration at A shows a flanged shell after the drawing operation. A trimming die is required to trim the irregular edge of the flange . The shell is placed over a locating plug B and descent of the upper die causes the scrap ring to be cut from around the flange. After trimming, the shell is carried up in the

B

upper die and a positive knockout ejects it near the top of the stroke. The scrap rings are forced down arou nd the lower trimming punch until they are split in two by scrap cutters C applied at the front and back of the die. The scrap pieces fall to the sides, away from the operator of the press.

20-5. PIERCING DIES Piercing dies pierce holes in stampings. There a re two principal reasons for piercing holes in a separate operation instead of combining piercing with other operations: 1. When a subsequent bending, forming, or drawing operation would distort the previously pierced hole or holes 2. When the edge of the pierced hole is too close to the edge of the blank for adequate strength in the die section. This occurs in compound and combination dies in which piercing and blanking are done simutaneously. In the inset a t A is shown a flanged shell requiring four holes to be pierced in the flange. If the holes we re pierced before the drawing operation they wou ld become distorted because of the blankholder pressure applied to the flange in the drawing process. The shell is located in an accu rately ground hole in the die block . Piercing punches are retained in a punch plate fastened to the punch holder, and a knockout effects stripping after the holes have been pierced.

C

A

Fig. 20·4. Trimming die.

240

TYPES OF DIES

B

A Fig. 20·5. Piercing die.

20·6. SHAVING DIES Shaving is the operation of removing a small amount of metal from around the edges of a blank or hole in order to improve the surface. A properly shaved blank has a straight, smooth edge and it is held to a very accurate size. Many instrument, business machine, and other parts are shaved to provide better functioning and longer wear. In the illustration, a blank A is to be shaved, both along outside edges and in the walls of the two holes. The shaving die for this workpiece consists of an inverted shaving punch B fastened to the die

Fig. 20·6. Shaving die.

holder, and a shaving die block C fastened to the punch holder. A s pacer D backs up the die block and it retains the shaving punches for the holes. The blank is located in a nest E beveled to provide clearance for the curled chip. The nest is mounted on a spring stripper plate guided on two guide pins F. The shaved blank is carried up, held in the die block with considerab le pressure, and it is ejected near the top of the stroke by a positive knockout. Shaving dies are ordinari ly held in floating adapter die sets for better alignmen t. This is necessary because no clearance is applied between punches and die block.

TYPES OF DIES

241

D

c

A

Fig. 20·7. Broaching die.

20-7.

BROACHI~G

DIES

Broaching may be considered to be a series of shaving operations performed one after the other by the same tool. A broach is provided with a number of teeth, each of which cuts a chip as the broach traverses the surface to be finished. Internal broaches finish holes ; surface or slab broaches finish outside surfaces. Two conditions make broaching necessary : 1. Blanks too thick for shaving. Considerable metal must be removed from the edges of thick blanks and a series of shaving dies would be required for a smooth finish to be produced. It is then less expe nsive to build a broaching die. 2. When considerable metal must be removed. This occurs when ridges or other shapes must be applied in the edges of the blank. It is often i mpractical to blank such shapes directly because the cutting edges would be weak and subject to breakage. In the illustration, a blank at A must have small pointed serrations machined in the sides. The die is provided with two broaches B supported during the cutting process by hardened backing blocks C. The blank is located in a nest D composed of two opposed plates machined to fit the contour. Pressure pad E, backed up by heavy springs, clamps the blank securely before Cl!tting begins. The first three or four teeth of the broach are made undersize and they ordinarily do no cutting except if an oversize blank is introduced into the die . The last three or four teeth are sizing

teeth. Intermediate teeth are called working teeth and they take the successive chips to machine the serrations.

20-8.

HOR~

DIES

A horn die is provided with a projecting post called a horn . Bent, formed, or drawn workpieces are applied over the horn for performing secondary operations . In the illustration at A, a blank has been reversebent in a previous operation and the ends are to be hooked together and seamed in a horn die. The horn B is retained in a holder C fastened to the die holder. When the ram descends, seaming punch D strikes the workpiece to form the seam . Many other operations such as piercing staking, and the like are also performed in horn dies.

20-9. SIDE CAM DI ES Side cams transform vertical motion from the press ram into horizontal or angular motion and they make possible many ingenious operations. In the illustration at A, a flanged sh ell requires two holes pierced in its side. The shell is placed over die block B of the die. Descent of the upper die causes pressure pad C to seat the shell firm ly over the block. Further descent causes side cams D to move the punch- carry ing slides E for piercing the holes. Spring strippers F strip the shell from around the piercing punches as they are withdrawn.

242

TYPES OF DIES

Fig. 20-8. Horn die. F

E

B

A

8

F

Fig. 20·9. Side cam die.

TYPES OF DIES

243

B

D

A

E

Fig. 20-10. Bending die.

20-10. BENDING DIES A bending die deforms portions of flat blanks to some angular position. The line of bend is straight along its entire length, as differentiated from a forming die which produces workpieces having a curved line of bend. In the illustration, a flat blank is to be given a double bend to form a U shape. The blank is inserted in gages A fastened on bending blocks B. The bending blocks, in turn, are fastened to the die holder. Upon descent of the upper die, the bending punch C grips the blank between its lower face and pressure pad 0. Pins E extend to the pressu re attachment of the press. Shedder F strips the workpiece from the punch.

20-11. FORMING DIES The operation of forming is similar to bending except that the line of bend is curved instead of straight and plastic deformation in the material is more severe. In the illustration the flat blank at A is to be formed into a part having a curved contour. The blank is positioned in nest B composed of two plates mounted on pressure pad C. When the ram descends, the blank is gripped between the bottoms of forming blocks D and the surface of pressure pad C. Further descent causes the sides of the bl ank to be formed to the curved shape of forming blocks D and formin g punch E. At the bottom of the stroke, knockout block F applies the final form. It bottoms against a hardened spacer fastened to the punch holder thus "setting" the form. When the die

ascends, the part is carried up within form blocks D. Near the top of the stroke it is ejected by knockou t F.

20-12. DRAWING Dl ES The operation of drawing is similar to forming, although usually there is more severe plastic deformation in the material. The difference between the two occurs in the extent of closure in the form. Consider a drawn cup such as a metal drinking cup. The material extends all around the sides and therefore the part is said to have been drawn. In a formed part the material does not extend completely around to surround a space, even though the formed contour may be quite intricate. In the illustration at A, a flat disk is to be drawn into a cup. The blank is placed on pressure pad B of the drawing die and it is located by four spring-loaded pins C. Descent of the upper die causes the blank to be gripped securely between the surface of pressure pad B and the lower surface of draw ring D. Further descent of the ram causes the blank to be drawn over punch E until it has assumed the cup shape shown in the closed view at the right. Pressure pins F extend to the pressure attachment of the press. The amount of pressure must be adjusted carefully. Excessive pressure would cause the bottom of the cup to be punched out. Insufficient pressure would allow wrinkles to form. With the proper amount of pressure, a smooth, wrinkle-free cup is produced. Drawing is extensively used for producing stampings ranging from ti ny cups and ferrules to large shells for pressure vessels, ships, aircraft, and missiles.

244

TYPES OF DIES

E

C

B

Fig. 20·1 1. Forming die.

Fig. 20·12. Drawing die.

TYPES OF DIES

2!5

A

Fig. 20·13. Curling die.

20-13.

CURLI~G

DIES

A curling die forms the material at the edge of a workpiece into a circular shape or hollow ring. Flat blanks may be curled; a common application is a hinge formed of two plates each of which is curled at one side for engagement of the hinge pin. More often, curling is applied to edges of the open ends of cups and shells to provide stiffness and smooth, rounded edges. Most pans used for cooking and baking foods are curled. In the illustration, a drawn shell shown at A is to be curled. The shell is placed in the curling die where it rests on knockout pad B. Descent of the upper die causes the knockout pad to be pushed down until it bottoms on the die holder. Further descent causes curling punch C to curl the edge of the shell. Near the bottom of the stroke, the lip of the material contacts an an gular surface machined in curling ring D to complete the curl. When the punch goes up, the knockout raises the shell for easy removal.

20-14. BULGING DIES A bulging die expands a portion of a drawn shell causing it to bulge. There are two types: fluid dies and rubber dies. Fluid dies employ water or oil as the expanding medium and a ram applies pressure to the fluid. In rubber dies, a pad or block or rubber under pressure moves the walls of the workpiece to the desired position. This is possible because rubber is

virtually incompressible. Although it can be made to change its shape, the volume remains the same. In the illustration at A, a drawn shell is to be bulged at its closed end. The shell is placed over punch 8 ofthe bulging die and its lower end is confined in lower die C. The upper end of punch B is a rubber ring within which is applied a spreader rod D. This rod is conical at its upper end and it helps the rubber to flow outward to the desired shape. When the press ram descends, the upper die applies a force to the shell bottom and since the rubber cannot compress, it is forced outward bulging the walls of the shell. When the ram goes up, the rubber returns to its original shape and the bulged shell can be removed from the die. After bulging, a shell is shorter than it was previously.

20-15. SWAGING DIES The operation of swaging, sometimes called necking, is exactly the opposite of bulging. When a workpiece is swaged a portion is reduced in size and this causes the part . to become longer th-an it was before swaging. In the illustration at A, a shell is to be swaged at its open end. It is inserted in the swaging die where it rests on knockout pad B and its lower end is surrounded by the walls of block C. When the ram descends, swaging die D reduces a portion of the diameter of the shell and this becomes longer.

246

TYPES OF DIES

A 0

8

Fig. 20-14. Bulging die that employs rubber as the bul ging medium.

A Fig. 20·15. Swaging die.

TYPES OF DIES

247

A

Fig. 20·16. Extruding die.

20-16. EXTRUDING DIES The function of all the dies discussed so far is to perform work on sheet material - to cut sheet material into blanks, to perform further operations upon the blanks, or to perform operations on work pieces bent, formed, or drawn from the blanks. We come now to interesting classes of dies that perform secondary operations on small thick blanks called slugs. In these dies the slugs are severely deformed to make parts having no resemblance to the slugs from which they were made. The first class is called extruding dies. In this type of die each slug is partly confined in a cavity and extremely high pressure is applied by a punch to cause the material in the slug to extrude or squirt out, much like toothpaste is extruded when the tube is squeezed. In the illustration the slug A is to be extruded into a thin-walled shell having a conical closed end. The slug is placed in die block B, backed up by a hardened plate C. The bottom of the cavity in the die block is formed by the end of knockout rod 0. When the press ram descends extruding punch E first squeezes the material in the slug until it assumes the shape of the die cavity and of the working end of the extruding punch. Continued descent causes the material to extrude upward between the wall of the punch and the wall of the die cavity. The amount of clearance between the two determines the thickness of the wall of the extruded shell. The extruding punch is retained in punch plate F and because of the high pressure involved, it is backed up by backing plate G.

20·17. COLD FORMING DIES Cold forming dies produce workpieces by applying pressure to blanks, squeezing and displacing the material until it assumes the shape of the punch and die. In the illustration at A, a slug is to be formed into a flanged part in a cold forming die. It is placed on punch B located within spring-loaded V gages C. Descent of the upper die causes th e material under the upper die block to be displaced outward to fo rm the flange. As the flange increases in diameter, the gages are pushed back as shown. When the die goes up, the part is carried upward within it and it is ejected near the top of the stroke by knockout plunger D actuated by knockout rod E. 20-18. PROGRESSIVE DIES In a progressive die the strip is moved in stages from station to station. Different operations are performed on it at each station except at idle ones applied to provide room for components. A complete workpiece is removed from the strip at the final station . A.ll of the operations described previously may be performed in progressive dies. For example, a singl e die of this type may do piercing at the first station, trimming at the second station, bending at the thi rd, forming at the fourth etc. A progressive die may thus be considered as a series of different dies placed side by side with the strip passing through each successively. This analogy has some merit although i t does not give a true picture of the extremely close

248

TYPES OF DIES

c

Fig, 20·18. Progressive die.

A Fig. 20·17. Cold forming die,

interrelationship between the various stations. In the illustration at A, a pierced, trimmed and bent part is to be produced complete in a simple progressive die. At the first station the strip is notched and pierced and at the second station the blank is cut off and bent. You should easily recognize all of the elements in this die - the die block, piercing punch , trimming punch, knockout , stop block, and all the others,

20·19. SUB-PRESS DIES Sub-press dies blank and form very small watc clock, and instrument parts. An example would be -=small instrument cam shown at A. The die componen· are retained in a subpress which is, as its na e implies, actually a small press operated in a large. one. The sub-press is composed of base C, barre. e and plunger D. A long, tapered babbit bearing E pr vided with longitudinal key slots guides the plunger a.:J.~ prevents rotation. Tightening spanner nut F agains·

249

TYPES OF DIES

I

c

A

Fig. 20·19. Sub·preH die.

Fig. 20·20. Assembly die.

250

bearin g E caus es it to cl ose around plunger 0 to remove all loos eness. The top portion of pl unge r 0 is engaged by actuator G threaded into a central tapped hole . The slot of the ac tuator is engaged loosely by a yoke fastened to the press ram. Thus the press ram does not gui de the sub-press in any way . It simply applies the up a nd down motion. Sub-press dies are usually of the compound type because of the considerable accuracy obtained .

20-20. ASSEMBLY DIES by

Assembly dies assem ble two or more parts togeth er press-fitting, riveting, staking, or other means.

TYPES OF DIE

Components are assembled very quickly and relationsh ips between parts can be maintained closely . In the left inset are s hown a link and two studs that are to be riveted together in an assembly die . The studs are positioned in die block A and they seat on plungers B. The link is then positione d over the studs, the tu rned-down ends of the studs engaging in holes in the link. Descent of the press ram causes rivetin g punches C to deform the ends of the studs into the shape of rivet heads. A hardened plate D backs up the punches to prevent the heads from sinking into the relatively soft material of the die set. Another hardened plate E backs up th e plun gers.

INDEX A Accuracy in blanks, 52 Air hardening tool steel, 235 Allowance for trimming operation, note, 227 Allowances, application of, 87 for one-pass scrap strip layouts, 85 for two-pass scrap strip layouts, 87 minimum, 87 scrap strip, 85 secondary , 216 Angular edge blanks, 55 Area of blank , calculations for , 88 Area to be blanked, 57 Assembly dies, 19, 250 Automated press, 40 Automatic stop assembly, holes in stripper plate for, 155 Automatic stop holders, dimensions of, 155 Automatic stop proportions, relationship of stripper plate thickness to, 152 Automatic stops, 7, 67, 233 back gage thickness relationship to, 157 dimensions of, 155 end-acting, 151 fulcrum pins for, 158 set screw location in, 157 side-acting, 150 spring dimensions for, 158 spring plunger for, 152 stop holder for side-acting, 151 toe lengths of, 157 Automatic stops and holders, stand ardized, 155 Automatic unloaders , 40 Auxiliary punch shank, 170

B Back gage, 7, 232 Back gage and front spacer, 135 Back gage thickness, relationship to automatic stop, 157

Back gear assembly, 23 Backing blocks, 170 Backing plates, 112, 130 Back-post die sets, styles for, 203 Ball-bearing die sets, 193 Bar pusher, 137 Bend development, 217 Bend formulas, 218 Bending, 16 Bending dies, 243 Beveled gage pins, 138 Bill of material, 8, 73 conten ts of, 22 8 li s ' ng automati c stop in, 233 listi ng back gage in, 232 li sti ng bl anki ng punch in, 231 li sting components in, 230 listing die block in , 230 listin g die set in, 201, 234 listing fasteners in, 233 listing finger stop in, 232 listing piercing punch in, 231 listing pilots in, 232 listing punch plate in, 231 lis ting stripper plate in, 233 Bit punches, 115 Blank ing, 15 added cuts in, 55, 56 Blanking area, 57 Blanking dies, 237 Blanking enlargement, 93 Blanking punches, 6, 61, 103, 231 large, 105 proportions, 107 proportions of composite sections, 109 small, 102 Blueprints, 1 Blank layouts, 43, 44 Blanks, 88 accuracy of, 52 angular edge, 55 area calculations, 88 basic shapes of, 75 contour, 52 development, 217, 218 for cut-off dies, 44 251

Blanks (Cont'd) num ber per strip, 88 parallelogram shaped, 55 posi tionin g, 75, 89 production , 53 shapes basic, 75 sizes, 52 stripping, 166 trapezoidal , 55 triangular, 54, 55 types of, 52 Bli nd dowels , 185 Bliss super-high-speed press, 36 Bolts, stripper, 183 Boss bushings, 193 Bottom knockouts, 168 Break line application, 101 Broaching, 16 Broaching dies , 241 Bulging, 17 Bulging dies, 245 Burr si de of blank, 53 Bushi ng and quill, 131 Bushings, boss, 193 die , 94 guide , 192 punch plate, 119 Button head screws, socket, 181

c Cap screws, socket, 178 Cast die sets , views for, 200 Center, establishing the die-set, 196 Center inserts, 100 Center of cutting load, 198 Center of stripping force, 166 Center-post die sets, 204 Checking a scrap strip, 14 Circle shearing, 53 Clearances, application of, 214 excessive, 51 insufficient , 48 table of die, 214 Cold formi ng, 18 Cold form ing dies, 247 Comme rcial die sets, 188

INDEX

252

Composite blanking punch sections, proportions of, 109 Composite die sections, proportions of, 97 Composite layouts, 97 Composite punches, "Superior," 108 Compound dies, 15, 122, 136, 238 Conical springs in finger stops, 148 Contour of blanks, 52 Contour sawing, 53 Conveyor feed press, 29 Crankshaft assembly, 23 Curling, 17 Curling dies, 245 Cut off, 15 Cut-off die blanks, 44 Cut-off dies, 136, 238 Cut-off punches, punch plates for, 121 Cutting load center, 198 Cutting rings, 106 Cutting steels, 106

0 Damper, spring, 167 Deep drawing sheets, 47 Deformation, 46 Demountable guide bushings, 192 Design order, 10, 13 Detail drawings, 13 Detail number, 234 Development, mathematical method of, 222 of bend, 217 of blank, 217, 218 of drawn parts, 222 of formed part, 218 of shell, 222 of square and rectangular shells, 225 Double-row layouts, 75, 77 Di a l assembly, 3, 27 Dial presses, 26 hydraulic, 30 straight-sided, 32 Die block, 5, 59, 90, 211, 230 projections in, 202 proportions , 144 split, 94 standardization , 93 Die bushings, 94 Die clearances (tabl e), 214 Die components, typ es of, 230 Die cushion, 37 Die drawing, 228 Die fasteners, 173 Die feed, 38 Die holders, 190 thicknesses of, 206 Die operations, 14 Die parts , 3 Dies, ass embly, 19, 250 bendin g, 243

Dies (Cont'd) blanking, 237 broaching, 241 bulging, 245 cold forming, 247 compound, 122, 136, 238 curling, 245 cut-off, 136, 238 design of, 13 drawing, 3, 244 extruding, 247 forming, 244 hom, 122, 241 inverted, 164 piercing, 239 progressive, 14, 247 punch plates for inverted, 122 shaving, 141, 240 side-cam, 122, 241 sub-press, 248 swaging, 245 trimming, 239 Die sections, 96 proportions of composite, 97 Die segmen ts , 101 Die-set center, establishi ng the , 196 Die set components, 189 Die set, drawing the, 199 Die set machini ng, 201 Die s et stamp, 201 Die sets , 2 , 70, 234 ball-bearing, 193 center-post, 204 commercial, 188 dimensions not usually shown, 198 floating adapter, 205 four-post, 203 heavy-duty, 206 large semi -steel, 205 large steel, 206 listing in bill of material, 201 long narrow, 204 materials for, 188 precision, 188 round , 204 sectioning, 200 selection, 189 semi-steel, 188 special, 206 specifications fur, 194 steel, 188, 200 s tyles for back-post, 203 two-post, 202 three-post, 203 views for cast, 200 views for steel, 200 Die trigonometry, 210 Dimensioning, triangles in die, 211 Dimensions and notes, 8, 73 Dimensions, identifying calculated , 225 Dimensions of holes , 218

Dimensions of parts, 211 Disappearing pins, 139 Double roll feed, 39 Doweled punch head, 118 Dowel holes, reaming, 185 Doweling hardened parts, 186 Dowels, 184 blind, 185 diameter of, 186 for multiple parts, 185 Meredith, 186 ove rsizes in, 184 proportions of, 185 relieved, 185 Richard Brothers', 186 semi-blind, 185 shape of, 184 shear strength of, 184 strength of, 184 surface finish of, 184 through, 185 Drawing, 13, 17 reading a part, 227 screws on the, 176 the die, 3, 228 the die set, 199 th e part, 3, 42 the pilot, 126 Drawing dies, 244 Drawn part development, 222 " Durable" punches an d s leeves, 11S Dutchman, 118, 134

E Edge contour of strip, 51 Electric presses, 32 End-acting automatic stop, 151 End-wheel presses, 29 Enlargement, blank, 93 Ejecting cups and shells, 167 Evaluating results, 81 Extruding, 17 Extruding dies, 247

F Fasteners, 8, 69, 233 application of, 17 4 die,l73 force on, 176 spacing of, 175 threaded, 174 type of, 174 Fastening die steels, 99 Fastening, distance between holes, 175 Fastening long narrow parts, 176 Fastening plates, 180 Fastening, proportions for , 176 Feed, die, 38 Feed direction, 193 Feed, hitch, 37 Feeds, roll, 38, 137 Feeding and strai ghtenin g, 39

INDEX

Feeding thin strips, 136 Finger stops, 7, 66, 232 beveling, 143 cons tru ct ion of, 142 dimensions of, 146 interferences in , 143 machining spring, 147 multiple, 143 operation of, 142 proportions of, 146 radial slots in, 149 return spring used with, 143 s lot machining dimensions of, 147 spring, 147, 148 spring stripper used with, 143 strip clearance used with, 146 use of, 149 Finish of sheets, 47 Five-station layout, 85 Flame cutting, 53 knockouts, 170 Flanged punches, 104, 175 Flat head screws, socket, 180 Floating adapter die sets, 205 Fluid springs, 163 Tay lor, 164 Fool proofing, 91, 176, 204 Formed part development, 218 Forming, 17 Forming dies, 244 Forming in the knockout, 168 Formulas for thread length, 178 Four-post die s ets, 203 Four-post presses, 33, 34 Four-post underdrive presses, 36 Frame assembly, 21 Front space r and back gage, 135 Front spacer thickness, 146 Fulcrum pins for automatic stops, 158

G Gage pins, beveled, 138 Gages, 65 back, 7, 135, 232 for shaving dies, 141 internal, 141 relieved, 140 Gaging, pilot, 140 pin, 137 radius, 140 v, 140 Gap-frame presses , 20 construction of hydraulic, 30 large, 26 operating, 26 Grain direction , 234 Guide bushings, 192 demountable, 192 Guided punch plates, 123 Guide pins, 169 Guide post arrangement, 194 Gui de post ends, offset, 192 Guide posts, 191

53 Gu iding in the knockout, 167 Guiding in the s tri pper, 111, 130 Guiding the quill , 115

H

Knockouts (Cont'd) spider, 170 spring, 169, 171

L

Harden and grind note, 226 Hardening c racks, avoiding, 235 Heavy -duty die sets, 2CX'i Hi gh-carbon , high-chromium tool s teel, 235 High-carbon stee ls, 236 High-speed press, Bliss super, 36 High-s peed steel, 235 Hitch feed, 37 Holders , die, 190 punch, 189 Hole dimensions, 218 Holes, for screws, 177 for stripper bolts, 183, 202 reaming dowel, 185 Horn dies, 122, 241 Homing, 16 Homing presses , 29 Hot rolled sheets, 46 Hovis punches, 114 Hovis punch plates, 121 Hydraulic presses, 30 dial type, 30 s traight-sided type, 32 Hy droform presses, 35

Layouts, 13 altering, 83 blank, 43, 44 completed, 78 completed scrap strip, 83 composite, 97 correcting, 77 double-row, 75, 77 enlargement in, 212 evaluating, 82, 83 five-station, 85 j ig borer, 216 part, 76 pierce and blank, 79 scrap strip allowances for onepass, 85 scrap strip allowances for twopass , 87 strip, 43, 45 testing, 81, 82, 83 three-station, 84 triple-row, 76 Locatio g pads, 139 Lock screws, socket, 182 Low-carbon steels, 236

Indi rect knockouts , 122, 169 Indirect pilots, 129 conditions for, 129 small, 130 Individual punch plates, 120 Inse rts, 101, 104 Internal gages, 141 Inverted dies, 164 punch plates for, 122 Inve rted punch holders, 189 Iron hand unloader, 40 Irregular pilots, 129 Irregular punches, 117, 120 multiple, 120

Machi ne data sheet, 13 Materials, 46, 234 Mathematical method of development, 222 Mathematical relationship s, 208 Mating flats, 117 Medium carbon steels , 236 Meredith dowels, 186 Mis-feeds, 132 Missing dimensions in die sets, 198 Multiple finger stops, 143, 149 Multiple irregular punches, 120 Multiple parts, dowels for, 185 Multiple stock pushers, 149

M

J Jig borer layout,211, 216

K Keyed pilots, 133 Keyed punches, 120 Key for retaining irregular punches , 117 Keying the punch, 103 Knockout plates, spider, 170 knockout plungers, 171 Knockout rods, 171 Knockouts, 166, 202 bottom, 168 flame-cutting of, 170 forming in, 168 guiding in, 167 indirect, 122, 169 operation of, 166

N Narrow-run positioning, 76 Nesting, 77 Nibbling, 53 Non-sticking guide posts, 191 Notchin g, 56 Notching punches, 122 Note, allow for trimming operation , 2 27 develop blank, 227 die must produce part to print, 227 harden and grind, 226 shave entire contour, 22 7 sprin g-back allowance, 227 tool identification, 226 work to part print, 226 work to template, 227 Notes and dimensions, 8, 73 , 225

INDEX

254

0 Offset guide post ends, 192 Oil hardening tool steel, 23 5 Operation sheet, 13 Oversize dowels , 184

p Parallelogram shaped blanks, 5S Part dimensions, 211 Part drawing, 3, 42 readin g a, 227 Part layout , 76 Part na me, 234 Part prin t, 13, 76 Peening pilot heads, 131 Peening the punch he ad, 114 Perforating, 114 Perforators, step, 114 Perforators with quill, 115 Pierce and blank layouts , 79 Piercing, 15, 57 sp lit-level , 113 Piercing dies, 239 Piercing pun ches, 6, 62, 103, 231 Pilot gaging, 140 Pilot head, fl a t on, 133 Pilot head peening, 131 Piloting, conditions for indirect, 129 in heavy strips , 133 methods of, 129 Pilot nuts, 126 Pilot proportions, 126 Pilots, 7, 64 , 232 drawing, 126 indirect, 129 i rregu lar, 129 keyed , 133 large , 127 pinned, 134 press fit, 127, 129 quill, 131 set screws for backing, 127 set screws fo r holding, 131 shoulder , 125 small, 127 small indirect, 130 spring-backed, 131, 132, 162 Pin gagin g, 137 Pinned pilot, 134 Pins and stop collars, pressure, 169 Pins, guide, 169 Pin stop, 158 Pla tes , fastening, 180 Pneumatic die c us hion, 37 Pneumatic presses, 32 Positioning blanks, 75, 89 Positioning, narrow run, 76 wide run, 76 Posts, guide, 191 Power for presses, 20 Precision die sets, 188 Press accessories, 37 Presses, all-steel four-post, 33

Presses (Cont'd) automated, 40 Bliss super-high -speed, 36 construction of, 20 conveyor feed, 29 data on, 194 dial, 26 elect ric, 32 end-wheel, 29 four-post, 33 four-post underdrive , 36 gap-frame, 20 homin g, 29 hydraulic, 30 hydraulic dial, 30 hydraulic straight-sided, 32 hydroform, 35 large four-post, 34 large s trei gh t-sided, 33 pneumatic, 32 power of, 20 punch, 2 safety stop and trip assembly on, 29 speed of, 20 straight-sided, 32 straight-sided dial, 32 super- high-speed, 36 transfer, 34 underdri ve, 36 Press fit pilots, proportions of, 129 Press reclining mechanism , 25 Press speed, 20 Pressure pins and stop collars, 169 Print, part, 76 Prints, 14 Progressive dies , 14, 247 Progressive operations, 18 Projections in a die block, 202 Proportions, blanking punch, 107 composite bl anking punch section, 109 composite die section, 97 dowel, 185 fastening, 176 pilot, 126 press fit pilot, 129 Providing for shear in round punches, 108 Punches and sleeves, Durable, 115 Punches, bit, 115 blanking, 6. 61, 103, 231 flanged, 104, 175 for long slots, 104 Hovis, 114 irregular, 117, 120 keyed, 120 large, 112 large blanking, 105 multiple irregular, 120 notching, 122 piercing, 6, 62, 103, 231 proportions of blanking, 107 providing fo r shear in round , 108

Punches (Cont'd) punch plates for cut-off, 121 punch plates for single, 119 Richa rd Brothers', 113 sectioning large, 105 set screw holds, 112 set screws back up , 112 shoulder, 111 small blanking , 102 stepping small, 113 Superior composite, 108 Punch head, doweled , 118 Punch head peening, 114 Punch holders, 189 inverted , 189 thicknesses of, 206 Punch keying, 103 Punch plates, 6, 63, 231 bushings for, 119 for cut-off punches, 121 for inverted dies, 122 for single punches, 119 guided, 123 Hovis, 121 in dividual, 120 machining of, 162 purchased, 124 standardized, 121 stepped, 121 thicknesses of, 121 Punch press, 2 Punch-retaining set screws, 181 Pun ch sections, 108 proportions of composi.te blanking, 109 Punch shank, 190 auxiliary , 170 Purchased punch plates, 121 Pusher, bar, 137 roller, 137 spring, 139 stock, 137 Q Quill and bushing, 131 Quill pilots, 131 Quills, guiding, 115 spring-backed, 132 support of, 115

R Radius gaging, 140 Ram assembly, 22 Reclining mechanism, press, 25 Removable guide posts, 191 Retaining key for irregular punches, 117 Richard Brothers', dowels , 186 punches, 113 Right trian gles, 207 Rivets, 186 Roller pusher, 137 Roll feeds, 38, 137 double, 39

55

INDEX

Roll feeds (Cont'd) drives for, 39 operation of, 39 Rotating the strip, 79 Round die sets, 204 Round sectional die blocks, 101 Route sheets, 10 Routing, 53 Rubber shedder, 116 Rubber springs, 163 Rubber stamp for die set, 201 Running the strip, 78

s S.A.E. numbering system of steels, 236 Safe strength of screws, 183 Safety stop and trip assembly on presses, 29 Scrap strip, 1, 3, 5, 59, 74, 211 allowances, 85 allowances for one-pass lay outs, 85 allowances for two-pass layouts, 87 checking, 14 for five-station die, 85 for three-station die, 84 testing the, 80 trial, 80 Screws, application of, 180 designation on drawings, 176 force on, 176 holes for, 176 point styles for set, 181 proportions of socket cap, 178 punch-retaining set, 181 safe strength of, 183 shoulder, 182 socket button head, 181 socket cap, 178 socket flat head, 180 socket lock, 182 socket set, 181 square-head set, 182 Sectional die blocks, round, 101 Sectioning die blocks, 99 Sectioning die sets, 200 Sectioning large punches, 105 Section line spacing, 201 Sections for slots, 100 Semi-blind dowels, 185 Semi-steel die sets, 188 large, 205 Set screws, for backing up the pilot, 127 for backing up the punch, 112 for holding the pilot, 131 point styles for, 181 punch-retaining, 181 socket, 181 square-head, 182 Shave entire contour note, 227 Shaving, 16

Shaving dies, 240 gages for, 141 Shear, 94 application of, 107 theory of, 48 Sheared edges, 47 Shearing, 42 circle, 53 square, 53 with round die blocks, 96 Shear strength, 57 of dowels, 184 Shedders, 107, 116 rubber, 116 Sheets, cold rolled, 46 copper bearing, 46 deep drawing, 47 finish of, 47 hot rolled, 46 medium-carbon, 46 pickled and oiled, 46 sizes of, 43, 45 stretcher-leveled. 47 tempers of, 46 Shell bottoms, 222 Shell development, graphical method, 222 square and rectangular, 225 Shock resisting tool steel, 235 Shoulder pilots, 125 Shoulder punches, 111 Shoulder screws, 182 Side-acting automatic stop, 150 Side-cam dies, 122, 241 Side-cam operations, 16 Silicon steel, 47 Size of blank, 52 Sleeves and punches, "Durable", 115 Slitting, 42 Slots for slugs, 202 Slotted pilot nuts, 126 Slug slots, 202 Socket button head screws, 181 Socket cap screws, 178 Socket flat head screws, 180 Socket lock screws, 182 Socket set screws, 181 Soft plugs, 113 Solid strippers, 59 Spacer washers, 163 Spacing guide, 175 Spacing of fasteners, 1'15 Spacing of section lines, 201 Specifications of die sets, 194 Speed of presses, 20 Spider knockouts, 170 Split die blocks, 94 Split-level piercing, 113 Spring-actuated knocko uts , 171 Spring application in finger stops, 148 Spring-back allowance note, 227 Spring-backed pilots, 131, 132

Spring-backed quills, 132 Spring damper, 167 Spring dimensions for automatic stops, 158 Spring finger stops, 147, 148 conical springs in, 148 machining, 147 Spring knockouts, 169, 171 Spring pilots, 162 Spring plunger for automatic stops, 152 Spring pushers., 139 Springs, fluid, 163 rubber, 163 stripper bolt, 162 Taylor fluid, 164 Spring strippers, 160 Spring stripper used with finger stops, 143 Spring units, "Strippi t," 163 Square-head set screws, 182 Square shearing, 53 Stampings, 1 Standardized automatic stops and holders, 155 Standardized die blocks, 93 Standardized punch plates, 121 Steel die sets, 188, 200, 206 Steel, high carbon, 236 high speed, 235 low carbon, 236 medium carbon , 236 silicon, 47 tool, 235 . Stepped punch plates, 121 Step perforators, 114 Stepping small punches, 113 Stock pushers, 137 and multiple finger stops, 149 operation of, 148 Stock reels, 39 Stop collars and pressure pins, 169 Stop holder for side-acting automatic stop, 151 Stops, automatic, 7, 67, 233 finger, 7, 66, 232 Straight-side presses, 32 dial, 32 hydraulic, 32 large, 33 Strength of dowels, 184 Strength of screws, safe, 183 Stretcher-leveled sheets, 47 Strips, 44, 46 edge contour of, 51 equalizers of, 137 evaluating, 81 feeding thin, 136 for five-station die, 85 for three-station die, 84 layouts of, 43, 45 location of, 125 number of blanks in, 88 number per sheet, 43, 45

INDEX

256

Strips (Cont'd) positioning of, 130 rotation of, 79 running, 78 scrap, 1, 3, 5, 59, 74 Stripper bolts, 183 application of, 163 holes for, 183, 202 springs retained by, 162 Stripper plate, 7, 68, 233 for secondary operations, 160 thickness and automatic stop proportions, 152 Strippers, 68 guiding in, 111 machining punch openings in, 160 solid, 159 spring, 160 Stripper springs, short, 162 Stripping blanks, 166 Stripping force, 120, 165 center of, 166 "Strippit" spring units, 163 Styles of back-post die sets, 203 Sub-press dies, 248 Sub-press operations, 18 "Superior" composite punches, 108 "Superior" composites, 98 Surface finish of dowels, 184 Swaging, 17 Swagi ng dies, 245

T Taylor fluid springs, 164 Telescoping sleeve, 183 Tempers of sheets, 46 Testing the scrap strip, 80 Thicknesses of die holders and punch holders, 206 Threaded fasteners, 174 Thread engagement, minimum, 178 Thread length formulas, 178 Three-post die sets, 203 Three-station die, scrap strip for, 84 Three-station layouts, 84 Through dowels, 185 Toe lengths of automatic stops, 157 Tool identification note, 226 Tool inspection department, 11 Tool operation sheet, 10 Tool steels, 235 air hardening, 235 high carbon, high chromium , 235 oil hardening, 235 properties of, 236 shock resisting, 235 water hardening, 235 Transfer attachments , 40 Transfer presses, 34 Trapezoidal blanks, 55 Trial scrap strip, 80 Triangles, identification of sides and angles, 208

Triangles (Cont'd) in die dimensioning, 211 multipl e, 213 right, 207 solving adjacen t, 212 Triangular blanks, 54 Trigonometry, 207 die, 210 Trigonometric equations, 209 Trimming, 15 Trimming dies, 239 Trimming operations, 168 Trip assembly, 24 Triple-row layouts , 76 Turned bevels, 139 Two-post die sets, 202 Types of blanks, 52

u Unloade rs, automatic, 40 Underdrive presses, 36 four-post, 36

v V-gaging, 140

w Washers, spacer, 163 Wa ter-hardening tool steel, 235 Wedge block, 94 Wide-run positioning, 76

Die Design Fundamentals by Paquin

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